depends. Veiled gives you 5 or 10K for 5 kills (blind fire only) while Half Heath gives you 20k for 5 kills (Any way). Veiled lets you get extra $$ but not nearly as much as Half Heath. But its a trade off. With Half Health you die almost instantly.
i am about to be lvl 54, and invalid is definately worth it for lvls 52-54. it gives you ALOT of money. i recommend playing deathmatch because if you get 10+ kills you get 45,000 +, and the games are much quicker in deathmatch than plunder. thats what i think, based on my experience
Also for my second booster i put on (depending on the map) launch man or rocket man, which really helps with kills. the only thing you have to watch out for is at the beginning of the match, the rush for the power weapon, you just have to grab it, and QUICKLY blow the opponent up, or tactically destroy him before he gets to the weapon, and if you cant stop him, then grenade the weapon and you will then get a kill and the weapon... hope this helps, buddy!