Don't listen to the nay-says that insist that you won't be happy with whatever side you choose. The most important thing is that you play on a high population server. Both rebublic and empire will have enough players to find groups and decent guilds.
Figure out what kind of server you want (PvP, PvE, RP etc.), then choose a high population server that fits that criteria (the server status should be "Heavy" during your prime playing times). After that it's all up to your preference, each class has their own niche and I have found them all enjoyable.
PS - Trooper is fun, I don't think you'll be disappointed if that's what you choose.