Mass Effect 2 Vanguard Bonus weapon?

Well, what you're selecting is either Assault Rifle TRAINING or Sniper Rifle TRAINING vs. getting the Claymore Shotgun. That is, you won't get the Revenant AR or the Widow SR. Depending on how you feel about the stock ARs and SRs in the game... it might make your decision easier. Personally, I like adding SR training to the Vanguard (giving him some ability to take out enemies at long range). What the Viper lacks in power against the Widow, it makes up for in speed. I'm also quite comfortable using the Incisor, but I recognize that a lot of players really don't like that SR. I can still use the heavy pistol for mid-range and the SMGs and Shotguns at close range. The AR really only gives more rapid fire at mid-range, but I find the pistol works just fine for me.

I went with assault rifles, largely because I took sniper rifles in my first (Sentinel) playthrough and wanted to do something different second time around. The Mattock is fantastic as opuspace explained, it was the one I used the most. The Vindicator is very good for shooting things in the face after Charging.