Depends on how much you want to spend.
IMO the Palmer Daccapo is great and quite affordable.
It's better than the crappy Radial ProRMP, which is too quiet, and costs less.
Also you can adjust the output level on the Palmer, switch between -10/+4 and there's a ground lift.
If you can spend more, the Little Labs Redeye is also very popular.
What kind of interface do you have?
(I use a Torpedo Reload, but you already have a loadbox so it's overkill. Before I used the palmer)