Imps have the highs and the lows, and the Pubs have the **** subs who think Tionese gear is the pinnacle of PvP gear and is better than recruit gear.
I left around 1.2 and came back twice, after they put in legacy perks and then again right before 1.7. TOR is pretty forgiving if you wanna get back into the game honestly. Just find a good imp or pub guild to pvp with and take the week to grind out WH gear or grind PVE weeklies to get BH gear, you can be full 61 in no time and start doing HM EC and TFBs within the month.
GL finding a guild to really progress with the Expac on the horizon. At this point I'm just farming creds and WZ comms for 2.0. If you can't find what you want in live roll a toon in PTS til you find one you like, then spend the last months of 1.x grinding alts.
As for what faction, I'd honestly say Imps for real progression due to their overwhelming majority population wise. Pubs are cool, but there are so many bad subs. Guilds like <Jeejee> who are "pvp" guilds and suck harder than an overclocked hoover.