RE: What's the best engine for a Mini 3D?
You certainly can't go wrong with the .25 LA as I said, that's what I have. The APC 10x3 and 10x4 are what I'm using too. The LAs are light engines, the .46 LA is only 12.5oz with muffler and is a viable option in my opinion for those who want ballistic pull-out.
If you want to play it safe you can't go wrong with the .25LA