Personally, I feel the .52 Gal with Splash Wall and Killer Wail is the ideal setup for support. With the .52 Gal, you get the opportunity to lay down heavy coverage, decent distance, and it's got a kick to it that you can use as a "warning" to anyone approaching your area. Coupled with the Splash Wall, it's a perfect combination to control certain choke points on maps. For example:
(Credit to jCOnyx for an excellent map, in his competition strat thread here:
http://squidboards.com/threads/turf-war-competitive-strategies-control-points.633/ )
Typically on this map you want to control 1, 2, and your side of the map (the lanes coming from your H). For me, the best result has been blocking the main entrance leading into section 2. I do this by laying ink in an "X" pattern at the main entrance going into 2. This provides an early warning that enemies are coming, as they will be looking to cover your ink to advance. Once I feel they are close enough (but not too close of course), I throw down a Splash Wall to halt their progress. At that point, they have no choice but to shoot my Splash Wall or wait till it runs out. They cannot pass through it by normal means. The best part is that you can pass through it and shoot through it. Which gives you an immediate advantage, and leaves you with a couple of options.
1. Be offensive/aggressive and lay down more ink in the "X" pattern like before or go for a kill
2. Refill your ink as soon as you throw down your Splash Wall, to have another ready once it runs out (rinse,repeat)
Using this strategy has helped quite a bit since my team can super jump to me or cover the sections behind me as I defend the choke point. Obviously it isn't without flaws. The enemy team can just come over the walls from their lane or on either side of the Splash Wall, but in the heat of the moment, they're not really thinking strategies, and are usually more focused on pushing forward. That's not even including ways you can push back the enemy team with Killer Wail, while you setup some more or make a quick retreat to safety.
There's also a bit of strategy you can use on Blackbelly Skatepark with the Splash Wall...
Simply go to the center platform (the tall one in the middle), go to the very edge of the platform closest to your side (UP ARROW) , aim straight down and throw a Splash Wall towards the UP ARROW. It will land on the every edge and face towards the enemy side. Now you have a limited window to spray ink on the enemy side without immediate fear of being sniped or splashed. Watch your ink and surroundings though!
Sorry for the poorly slapped together pics and thought process. It's 1am and the bed is haunting my thoughts. Goodnight! Hope it helps!