Should start with Killbot. Self-heals are the most important skills in any RPG, in my opinion.
“Suck” is subjective. I think they did a fantastic job designing the character, since it’s random, annoying, and humorous, which really captures the essence of Claptrap. It’s also pretty effective. However I don’t really see the appeal of taking it beyond level 26. There are still useful skills in the I Love You Guys tree, but they’re not very exciting. Plus Load ‘n’ Splode is good, and Coincidental Combustion could be useful if you use non-explosive guns (perhaps to get some use out of Maniacal Laughter). But as far as I’m concerned once Claptrap can turn into a pirate ship, you’ve seen all the good stuff.
I took pretty much the opposite approach to KrewlraiN, very aggressive close range charges to get the most use out of the Start With A Bang novas and whatever shotgun I had at the time (Ravager is ideal, but sometimes all you have is a Hulk, Pounder, Coach Gun, etc.). The Too Scoops is insanely powerful with Clappy, and can carry you through most of NVHM if you want. Shoot at an enemy’s feet, it will probably freeze, the nova will shatter it, reload because it’s a single-shot gun, repeat. Doesn’t work on a lot of bosses though. And using a Ravager can give you the best One Last Thing combo - first shot, nova, massive OLT second shot, reload, repeat.
I viewed VaultHunter.exe as an emergency heal button. If a useful package came up, great, but otherwise I’d make the best of it. A tip for funzerking - spam melee once there are no enemies around, that way you don’t waste so much ammo.
One would think that Claptrap would have lots of interesting and unique dialog in Claptastic Voayge, but one would be wrong. CV actually makes no sense at all playing as Claptrap - I think somehow the developers forgot it was a playable character.