My favorite would be Heavy Handed, just because then I can set my Luck to 1 and focus on other SPECIAL statistics. Plus, I've grown to not rely on criticals when it comes to Melee and Unarmed.
Runner-up would be Good Natured because it adds points towards "general" skills at the cost of reducing "combat" skills you may not use.
I've taken Loose Cannon, Built to Destroy, and Kamikaze as well.
Loose Cannon is really only helpful at the start of the game for me. The only explosive you readily have available is Dynamite and you probably won't be using it for long range encounters.
Built to Destroy, while being really helpful at the end game, can cripple a lot of stuff early on. While I enjoyed using it, having to use to do more maintenance on my weapons as well as having Raul as a companion to offset the trait was a bit of a "eh". To be honest, Raul's pretty good with the
though so it wasn't all of a bad thing.
Kamikaze's actually alright throughout the game. The -2 DT really does little to no difference, especially since the enemies at the beginning of the game just break through your DT anyways, even with the addition 2 DT. Gaining 10 AP is pretty important for those V.A.T.S. heavy people as you can't exactly pull a 250+ AP trick in New Vegas anymore.