well that is completly dependant on your riding style. if your doing more street, park and your back wheel is taking alot of hits 24" would be better as its alot stronger. it would also save a gd amount of weight. i personally prefer 24" as my bike was alot easier to do tricks on, throw around ect. if your more of a dj, trails rider or bit of dh i would defo stick with the 26" man. btw if you are planning on going 24" dont buy a complete, your better buying a Frame and building it up i would reccomend blk mrkt or ns. hope this helped.
but its very hard to work this out, without taking the plunge and actually getting a 24" if you are currently riding a 26"
unfortunately borrowing a bike won't tell you much, as it takes time to adjust and get the most from the change
personally I owned several 24" bikes (DMR, identiti, etc.) and eventually went back to 20" (BMX) for street and park, and got a 26" for dirt jumping and everything else
something else I would say from experiences
I found 24" wheels work the best on 24" specific frames!
many brands advertise as 24"/26" compatible but you don't get any real benefits from running 24"s on one of these frames as you end up with a long back end and the bottom bracket height can feel wrong, compared to 24" specific frames
im running a ns traff with 26's on. came from a tranny 24 and sub 24 before that. 26 has been by far the nicest thing to ride. its all about the geometry of the frame and how the bike is set up. never put 24's on a 26 frame, the bb is too low and the bike will be long compared to such as 24 specific frames. i see a lot of people swiching to 24 because they think it will spin easier but like i said its more about the geometry than anything
As others have said, it really depends on personal preference. I always rode 26's, took the plunge and went to 24'' and found a lot of things a lot easier, spins, whips and anything that requires you to move your bike around in the air is technically easier to do, your bike becomes more 'chuckable', so I learned stuff like 360's relatively quickly after struggling for ages on 26's. As caravanking said, it's also very much about the geometry of the frame and how suited it is to 24's. I run a Leaf OS (essentially a long D.one) and its got a short back end so didnt fare too badly with them.
However, my style suffered and I found i wasn't half as smooth or consistent as I was on 26's, probably cos I'm a lanky unbalanced rider, so I've recently swapped back and I'm enjoying the confidence and stability it's given me.