Personally:
FFA: this seems too chaotic for me, there is too much going on the screen, rarely skill-based
Team: now this is what i started playing today and most likely will play this only with how currently its working, random teams totally don't mean a bad thing as long as you can restrain yourself from the if-you-have-a-free-bomb-set-it-as-fast-as-you-can syndrome, friendly fire sucks, i understand that some can't stand it, i respect that; sometimes you get really good synergy with random people, this is massively positive, more than steamrolling on FFA, the bad thing for people can be that the rank points are poor here but seriously, the experience is extremely positive as long as you are willing to try to break the first walls
GvG: not touching this even if you pay me, not my cup of tea due all the other GvG experiences i had in other games, while here we are really massively protected by the GMs some stuff will still go through, plus its easier to stack and steamroll others and i don't feel like looking for people on my level because its Guild vs Guild so it comes super competetive
And generally my experience was bad at start, all the lag, getting inside my own bombs locked northeast on them, this really had my blood boiling from the rage but after some crude experiences i managed to adapt to some point and since i play Team only it doesn't obstruct me as much as it did in FFA. The server-side lagspikes are annoying still but i see that the staff is working on it (reboot today for example) so i hope for the best. And the bribe not working properly is also sucky, it ate like 50 energy from me at one bribe when i paid only 4 or so. But i'm not gonna blame anyone else than me on that, since i read the message about it not working properly, i risked, i sucked up my own fault. Hopefully we can get European servers seeing how the game is hosted on Amazon's EC2 and they have european datacenters.
And a small speculation about the next-to-come PvP gamemode, since its called Lockdown i think it will be about locking down areas, some kind of Domination-esque gamemode, something akin to Team Fortress 2's infamous map - tc_hydro but with variation, something like this map for TF2 - http://www.gamebanana.com/maps/107047
Team, players skills are more balanced. You get more chance to get 2 token (winner as a team not a single player).
I think the winning key on this game is not to get yourself killed too often.