Looking at my Battlefield 3 battlelog, I put many more hours into assault and support than I remember. I expected my percentages to Engineer > Support > Assault > Recon, but it's more Support > Assault > Engineer > Recon, with about 10% drops between the first three. Support probably comes from me playing the bigger maps like Caspian and Firestorm more than others, and the hilarity of using a bipod LMG against fucking sniping recons. Yes, you stupid shits, I can hit you with pinpoint accuracy from the same distance and with an automatic. Suck it.
My play time for the Battlefield 4 beta was heavily in favour of Engineer. Probably went Engineer > Assault > Recon > Support. In a map like Siege of Shanghai Engineer really shined, urban encounters close enough for SMGs to work their magic and the frequent use of vehicles making rockets invaluable for the team. Assault was just me getting a feel and enjoying the shooting. Recon because I like that they've got C4 now. And Support way down the list because the default LMG sucked balls.
This would be awesome. Cheers.