Interestingly enough, I got directed to Savage when I described Trem to another friend. And then they made Savage fully free just last month or so... so it's also sitting on my HDD

I've played both, but I still highly prefer Trem. Trem is tight, close-confine fighting. It doesn't require "better levels" so much as better skill.
That said, Savage does have its advantages, including a researchable tech tree, multiple items, their commander/RTS view is actually pretty spiffy (Make that VERY spiffy considering all the action that's really going on on-screen) and their own neat humans vs. monsters system.
Each has its own strengths, but I think my engineer will stick to Trem
