Inflatable or self-inflating mats are the best camping mat choice if you're off on a multi-day trip, as they're typically much more comfortable when inflated and pack down smaller when not in use – you'll be able to pop them inside your hiking backpack rather than strapping them to the outside. There is, however, always a slight risk of puncture (choosing a pricier model is always a good idea here).
Choosing inflatable camping mats can be a complex task, as the various materials and construction make a massive difference to the insulation they dish out – yes, even from two mats that look very similar. As usual, the cheaper the mat, the less insulation you'll probably get, and be sure to check the R-value.
Simple foam camping mats shouldn't be dismissed entirely, though. They're both cheaper and more robust but less comfortable than their inflated brethren. In fact, they're pretty much indestructible, so they are ideal for festival use or trekking in particularly rugged terrain that would slice an inflatable to shreds. While bulky, they're very lightweight and unbothered by getting wet, too.