So,

I've heard a lot of good things about the spring engine, and how it's specialized for RTS, but it's still a bit nitch.

Does anyone have any 1st hand experience with using this engine?

We were originally going to use Unreal, but I'm now reconsidering. and going back to the research stage.

Any insights would be appreciated.

Engines are not a Game Design topic. You should know that, general. Thread moved to the appropriate forum for “which engine” and “best engine” questions.