Shimano Deore XT M780 Shadow

Good part per cost if you're low end rider or burn through mechs

Pros
Perfect for a budget buy, typical Shimano performance you've come to expect.

Cons
Durability

Came factory on my 2016 Trek Xcal. So far, they have been very smooth and reliable. No complaints with performance.

Pros
Smooth. Durable

Cons
None

I changed to this after tearing up my X.9 Can tell a huge difference. Shifts very clean, even under pressure.

Pros
Weight
Smooth Shifting
Durability

Cons
None

I've used this for a full season and am very happy with it so far. I would buy this again, but I don't think I'll have to buy another derailleur for a few years.

Pros
Looks good, tough, smooth shifting

Cons
none

If you don't care on improving the gear usage in your 3x9, I suggest go with the mid-cage. Long cage is prone for more chain slapping.

Pros
Easy maintenance, great looking, tough.

Cons
Too much chain slap on long cage model.

Shimano upgraded me on my Fuel EX 8 from SLX to this XT and I love it. I blew through 2 SLX rear d's in just a few months. The XT is the way to go!

Pros
Tough, Smooth, Durable, Reliable, Easy maintenance

Cons
None Really