Apple's service is quite reliable. The site actually has limited advertising and has a clean layout which some other web mail services lack. Yet another email option is MacLaunch , a portal for Mac users. Their email is similar to MegaMac's, although their interface isn't as sleek. MacLaunch also includes lots of other features like stock quotes, news feeds, and discussion boards.
MacLaunch mail is also only web-based, no POP access.
Of course, for many people who travel or work at different computers web-based mail works out better because it can be accessed anywhere. In the world of free email there are many other choices, including the major players such as Yahoo and ZDNet. In the end, you'll have to choose which service is best for you. For traveling folks, web-based email works great.