In the hope of it being of use to someone I'll share a bit on London, Istanbul and Reading.

London is the central hub for everything in the UK. It has a weekday population of around 13 million and weekend population of around 9 million (due to commuters who stay during the week). I read somewhere that if London was a country on it's own it'd have the world's 7th biggest economy (although this was before the banking crisis).

PROS

You can do anything in the London. Seriously, anything. You can eat any food from anywhere in the world. Drink anything from anywhere in the world. Want to go skiing? It's about £90 to go to Switzerland from Stanstead airport. Alternatively you can go to Milton Keynes (about 45 minutes away) and go to the indoor ski slope with real snow.

Music, theatre, art, culture, history. Everything and I mean everything comes to or goes through London.

It's fairly safe for the most part, as long as you avoid the trouble spots.

Almost every large business in the UK, and most European/International businesses has a headquarters or office in London.

The transport system, despite our gripes is awesome compared to almost anywhere in the US (except from what I've heard about New York).

You can hire bikes by the hour to ride around London. Just walk up to the bike, put some money in, ride off on the cycle routes and drop it off at another lock.

The hacker scene is great. Hackspace, DC4420 and OWASP run regular meetings. There's a 2600 chapter for the kids.

Imperial College and UCL are great Universities to draw talent from. Oxford is an hour away, Cambridge a little more, Royal Holloway about the same. All have great graduates with various specialisms.

CONS

It's rammed. Everything is busy.

It's ridiculously expensive. Expect to pay a fortune if you want to live in zone 1 or 2.

There's a bubble a bit like SF. You don't really know if what you're doing is innovative or just masturbation.

While there's investment around, you'll have to look for it and it's not on the same scale as in the US. Having said that you're probably in the best place in Europe to find angels, given the amount of money floating around.

Reading

Reading is largely a commuter town about 20 minutes from London Paddington. It takes about the same time to get to London Paddington from Reading as it does from London Waterloo.

PROS

You're not in London. You don't have to deal with all the London set if you don't want to but it's close enough to get in when you want to.

Oxford is about an hour away. Holloway is about an hour away. UWE and Bristol Uni are an hour and a half away.

You're in what's known as 'Thames Silicon Valley'. Everything's cheaper than London, it's easier to reach London and there are heaps of smaller startups around here.

There's a good but significantly smaller tech scene. There's a local LUG, various small hacker meetups, but most go to London because it's so close.

Most acts pass through. In Reading I've seen Frankie Boyle, Massive Attack and a few other groups but also a lot of up and coming acts.

Reading Beer Festival is probably marginally better (but a bit smaller) than the Great British Beer Festival in London. The Reading Ale and Jazz Festival (RAAJ) is also great fun.

Loads of cycling routes and great rolling countryside make this great. You can actually ride to London if you wanted to over the National Cycle Network.

CONS

It feels like a suburb of London. That's not necessarily a bad thing.

Reading Uni's undergrad CS course doesn't seem to be that great.

It's cheaper but less connected to the money in London. If you're looking to self-fund Reading is a great place to grow. Not so much if you're looking for external funding.

Microsoft's main campus is in Reading, as is Oracle and a few others. That may seem a good thing but they're more or less constantly recruiting, making for competition in the employer department.

It's a small city/large town, so while there are some great places to eat/drink etc. there's a lot of crap too, so nights out tend to involve visiting the places you like, rather than something new all the time. Also London looms on the horizon and tends to pull you in now and again. This may be a good rather than bad thing, but it may make you pine for London.

Istanbul

As the world's only transcontinental city, Istanbul is truly where east meets west. On the eastern coast of Europe and the Western coast of Asia Minor, Istanbul is awash with money, although it lacks the investment infrastructure of London.

PROS

There is nowhere in eastern europe or asia minor other than Istanbul. All the money in Turkey goes there. It's probably the biggest thing until you hit Vienna in the west, Tehran in the east, Moscow to the north or Abu Dhabi to the south.

Great cuisine, nightlife (you go out on Friday evening and come home around 11am Sunday morning without stopping) and an improving public transport network make it a great place to live. Most large bands stop by Istanbul on world tours.

The history, culture, beautiful skylines (east looking west, west looking east) and architecture (contrast the skyscrapers with the minarets, Hagia Sophia and the Blue Mosque) are unlike anything anywhere else in the world. It's completely unique.

The people are the most amazingly friendly people you'll ever meet. Expect unparalleled levels of service compared to anywhere in the west. Turks are incredibly friendly people, it's toned down a bit in Istanbul but it's still way friendlier than London.

If you speak some Turkish it goes from being a beautiful but slightly scary city into being an absolutely incredible amazing place. The cultural customs may look a bit odd at first (as it does with any big city outside of the Anglosphere) but if you make the effort you'll be rewarded in spades.

There's a ridiculously high ratio of beautiful to ugly women (and men if that's your kind of thing). Head up to Nisantasi and watch the world go by with some Turkish Coffee.

The Princes' Islands are a great getaway more or less within the city limits. Buyukada (Big Island) is particularly stunning.

CONS

Turkish politics are a very complex beast. Never get involved. There's marches, protests, violence and of course the occasional bombing. Because Istanbul is the centre of the Turkish universe, everything happens here, including the bad. The same goes for football unfortunately.

As a city that knows it's the centre of the Turkish universe, it's so far up it's own arse it's unbelievable. In addition to the great, expect levels of pretentiousness that exceed London, especially amongst the 'sonradan gorme' set.

There's not much outside of Istanbul on anywhere near the same scale. Having said that check out Anatolia - Cappadocia, Bodrum, Antalya are all amazing.

There's a particular case of style over substance. Restaurants look amazing, have amazing service but when you want a rum, you're going to get Bacardi. If you want a Whisky, the best you'll get is Chivas Regal or Jack Daniels. Don't expect a great choice of beer. They have both kinds in most places - Efes and Tuborg.

Imported Alcohol costs a fortune. While Raki is great, Turkish wine generally isn't. Avoid Turkish spirits other than Raki. Turkish Vodka and Gin are terrible.

If you integrate into Turkish culture, the act of keeping up appearances can be quite stressful. It's all about wearing the right clothes, going to the right places and it's pretty sickening. It's not just for the upper classes, it permeates through a large part of the class structure.

Things are generally cheaper than most European countries, but are prone to currency fluctuations. Turkey is not in the EU, and while some of the EU directives have been implemented laws are more flexible than in Europe.

There is a degree of corruption in some places, but not in others. Navigating it and know where bribes are needed and where not can be difficult. It tends not to be a case of handing over envelopes filled with cash as much as bringing a bottle of 21 year old Scotch to the meeting as a gift for the decision maker. In this respect elements of Turkish customs, relationships and things that elsewhere could be seen as bribes can get a little muddy for yabancis.