The best scale for AFVs is probably 1/35. Because of space, though, I mostly do smaller scales, 99% of the times 1/72 or 1/76. 1/48 is a great scale for AFVs but there are very few kits available, other than the rare Bandai kits (except in Japan, apparently!) and a number of rather expensive kits in resin from France (some in 1/50). Academy and Zenghdefu both market moderm AFVs at 1/48, but the quality is not there. The Zenghdefu kits are motorized and feature the same running gear (on all kits!). Not too sure about the Academy, but they are motorized too.
1/72 and 1/76 have regained a lot of attention lately with many manufacturers releasing lots of new kits. Revell Germany, Hasegawa, and Fujimi are the ones bringing them back to limelight. The old(er) ESCI kits, if you can find them, are often great too. Also, tons and tons of 'garage' companies here in Europe producing myriads of less known subjects. !/76 is more popular in the UK, 1/72 in Continental Europe.
Another scale to consider is 1/87, namely Rocco Minitanks. Few parts in those kits but the quality is there and the range is quite amazing. Revell and Academy are currently releasing 1/144 minikits too, and I'm told they are nice. Then you can always go into really small stuff, 1/285... I've seen models and dioramas at that scale that were breathtaking!