I main .52 gal; I'm bad at basically every other weapon besides this and Junior, but it just fits so perfectly. Basically every loss I've had on .52 either involved an AFK on my side or me doing something dumb and giving the enemy an early advantage--and the latter situation I'm gradually learning how to turn around. Both the regular and the Deco version are very solid loadouts. Here are my thoughts:
General .52 Gal Play:
So this is where I've spent the majority of my time in Turf Wars. I have to say, if I were forced at Rollerpoint to make a Shooter tier list offhand right now, I'd probably stick this and Junior at the top (Junior is better at turf coverage, .52 is stronger in combat). Of course, making tier lists this early in the game is an exercise in futility--I've been mauled by my fair share of Aerosprays and SS Pros.
What I'm trying to say is that .52 Gal is really good. Anyway.
The opening for regular .52 Gal is this: get to mid as fast as your tech skill allows for. Actually, strike that--get to a spot that *has an advantage over mid* as fast as possible. The best example I can think of is the corridor on Arowana Mall, from which you can just barely reach a common sniper nest (be careful, I've been ganked there by observant charger players who presumably see my ink trail ahead of me) as well as put your wall in a decent spot. More on that in a moment. Substitute "mid" for any commonly contested areas on other maps--I've just got back from a ton of Mall games where this opener frequently got our team an advantage we could usually snowball into victory.
(One variation for larger maps is to forgo mid for a bit and go for an area that isn't usually hotly contested, such as zigzag on Saltspray Rig, and then take advantage of the fact that you now have a bunch of pathways to gank the enemy team from behind. You do enough DPS to get at least one kill by the time they actually react to your presence.)
Midgame, you'll want to look for areas with enemy paint and paint them. Obvious, right? Not only does this rack up a bunch of points, but with enemy ink comes enemy players. Generally you'll kill someone with 3 shots, maybe 2 if they don't have any defense upgrades or if you're packing offense upgrades (I think most players run defense, incidentally). When you're doing this, try to alternate between watching ahead of you for approaching players and watching the minimap to see if someone's painting behind you. It's harder than it sounds, but experience helps. (While I'm here, I'd like to recommend wearing headphones while you play, as that'll help you hear enemy gunfire faster so you can react quicker.)
Lategame, you're doing the same thing as you are midgame. By this point, the game has probably devolved into total chaos. Watch the minimap and try to hit opponents who lay a lot of ink. You're probably not the fastest ink-layer on your team--in fact, if your teammates are reasonably competent, you'll rarely have the highest score on your team. (And that's okay, provided you're still covering a reasonable area while also preventing the opponents from getting a foothold through kills and zoning.) Surprisingly, decisions get easier when there's little time left: if I attack this person and die, I will be gone from a significant chunk of the rest of the game; because my team is ahead, I can afford to camp this spot and get a kill that will prevent the Bad Guys from being able to come back; my team is behind, so I need to get kills quickly and safely so they have time to mount a comeback.
Deco Or No Deco?
The regular .52 loadout comes with Ink Wall and Killer Wail; the Deco comes with Seeker and Inkstrike.
With the regular loadout, you'll want to use Ink Wall in two ways: to cut off enemies from chokepoints (mid in Saltspray Rig is a great one; corridors on various maps are also good) and to protect yourself (drop one behind you to block potential ambushes from behind; throw one down in a 1v1 to stall while you reach a better position). Killer Wail is a powerful zoning tool as well: use it to force entrenched enemies out of their nests or to clear out a path to push into enemy territory.
The Deco loadout plays a surprisingly similar style; rather than block out enemies with stationary threats, you'll force them to get out of the way of your mobile, albeit ground-bound Seeker. Inkstrike is a bit more useful than Killer Wail IMO, since you can use it to assist from anywhere and it covers some ink (I saw on my minimap a teammate camping from a vulnerable spot on Arowana, so on a hunch I threw that Inkstrike in the ambush path; sure enough, I got a splat from it). Throwing out random Inkstrikes at enemy ink isn't horrible, since it does force the opponents to clean up the mess, but thoughtful use of it can be more impactful. Experiment some; I'm still pretty bad at Inkstriking, myself (and I'm personally more comfortable on the other loadout anyway).
Ultimately, both loadouts are good; this game is pretty well-balanced. Try both and see what works for you.
I haven't leveled high enough to check out the .96 gal yet, so I don't know if it's worth discussion in this thread or if it should get another.
It's 3AM; maybe I'll update later with map strats and perks and whatnot. (Protip: Stealth Super Jump is the best perk in the game.)