Good Question! I like to give my new toons somewhere between 50-100 mill as a starter. I found that's enough to make the journey to 50 much easier. Especially at the lower levels where having temp powers like the Grenade and Energy blast (I forget what it's called) Really help.
Depends on your planned usage and expectations. If you're farming using combine binds and expect to be near the 675% cap, then the double-hit is the way to go, otherwise the damage boosting will probably work better.