I have shot both extensively and still own both. I prefer the Eotech 551 for anything under 100 yards. It is super fast to pick up and I have not had trouble at all with the battery power. It takes only one push to turn on and will turn itself off after 4 or 8 hours(your choice) of nonuse. The only drawback to the Eotech that I have found is that it sits a little high on the gun and thus if you zero at 100 or even 50 yards, it shoots significantly low at close range.
The benefit I have seen on my Trijicon Reflex II (triangle) is that I can zero the point of the tringle at 100 or even 200 and the center or bottom of the triangle is still useful at close range. It also sits very low to the flattop mount and has the benefit of never having to worry about batteries. Mine has quick throw ARMS mount and I can take it off and on quickly and go back to almost perfect zero.
If you mount the Eotech on a quick release, it makes it even higher and the trouble with zero increases. They are both very durable and I would say that you can choose between shooting at a set distance with the Eotech or have the choice of close and long range with the Trijicon triangle.
By the way, I average about 2 inch groups at 100 yards with either set up. So they can be very accurate when set up properly.