From someone who has played and done well in both:
PRO FTP:
1) FTP's engine is more realistic, more random, and more fun. Tactically it is soooo much more open. You aren't restricted as much as in BT. No BT collapses, you don't need 5 bowlers or an allrounder, part-time bowlers can do the job if used well and lower order batsmen can score runs and aren't helpless. Experience, form, conditions, all play a bigger role than in BT.
2) Community is great. BT Sledging is essentially dead, while FTP's community is awesome, active, and fun. Atleast it was when I was there.
3) Training and youth system. You have a youth team, and you train all players with 1 net each instead of 10 nets to be spread over all players. It's a excellent system.
4) The game makes more 'sense', cricket wise. Fast bowlers and legspinners are better than medium pacers and offies, but are also rarer. You need strength to be a good quick/to hit more sixes, not necessary for a spinner. The conditions actually act like you expect them too. Batsmen and bowlers have no pre-determined 'nature', so can be set on any orders, but need the right skills and 'talents' for those orders. It's just that if you set a lineup in FTP going by common cricketing logic and no prior experience, you'll do well, compared to BT where you need to work the game engine, which doesn't always make sense.
- TONS of nations represented, so it's a lot more fun. I was part of the UAE and Bangla communities/nat teams myself.
ANTI FTP:
- Engine is too random. You often feel that, like Ste mentioned, orders have no effect. You lose control that you have in BT
- It doesn't have an active PC community.
- It's a LOT more complicated than BT, and as a result a lot more time consuming
FTP is the better game, but I prefer BT at the moment for the three reasons I've listed.