DS-877 = Good enough basic aerobatics. Not for hardcore 3D. It can't tail slide, and I'm nervous doing backward inverted with it. Surprisingly, it could lock the tail on hard climb outs. It doesn't like 6V and too much HS, proving the higher HS the more torque is needed.
Fut 3154 = I never had one, I don't intend to get one, due to low torque. And I hear people reporting it burning motor which doesn't suprise me, not enough stall torque IMO, although it's fast. For me it should be good for aerobatic park flyer plankers or maybe 400 class helis.
DS-577 = Great holding power. I'm very comfortable with it. Not too locked on sometimes, but with proper tweaking it is solid. I never experirenced the tail breaking away during hard maneuver. It's gonna stay on my Tr450 that's for sure.
HS-81 = Fast and torqueee. Not digital though. I never get to try it yet. For those who have experienced it. Please share your thoughts about it.
If you have the dough:
Fut 9650 = I don't have this on my Tr450, but I have it on my QJ8. This thing is rock solid even for this bigger than 450 class machine. If it can do well on my 8, it definitely gonna do well on on a 450. Due to it's popularity it can now be had for around $50 brand new, you just gonna have to do your research.
JR 3400G = I never had one. But judging through the factory specs this one is another overkill. Cost is way up there. Three years warranty, so if there's a failure within that period, you got an insurance. I heard JR has great custumer service.
If there's more servo you think would work or had good experience with. Please share us your thoughts.