Like others said it all depends on what you personally like and what feels comfortable to you. For me, my TCX Pro 2's are some of the most comfortable MX boots I've ever had on my feet. They are slightly wide, which fits my foot perfectly. The torsion control system (ie. hinged ankle) makes them fairly comfortable to walk in and allows for freedom of movement on the bike and trails. The downside to that (IMO) is a bit less stiffness for protection. I cased a triple back in April and hyper-extended both ankles. Would it have been better in different boots? Who knows... If/when I get back into MX I may pick up a pair of Gaerne SG10/12's or Tech 8/10's for a bit of extra stiffness and protection. I love the Sidi Crossfires - they are super well made - have a nice, low profile toe box, offer a hinged ankle as well, and probably have the best buckles out there - but I find them to be too narrow for my foot.
If I were mainly doing trail riding and not as much jumping, I'd definitely go for the TCX Pro 2.1's or the Sidi Crossfires - if you plan on jumping a lot I'd personally go for a non-hinged design like the new Tech 8 light, Tech 10, or SG 10 or 12.