Cyclic servos are one of the first thing you'll end up replacing in a crash. Why? Cause they're made of plastic. They work great, are pretty fast and accurate, last a long time, but are very delicate as far as crashes goes. So far, there are many alternatives which either uses harder plastic or metal gears. I prefer to use the metal gears as I have not damaged a single one in my long series of crashes since I installed them.
Here's what I recommend:
Hitec HS-65MG. They have metal gears, and are pretty accurate. (about 30$) On the cyclic, you should use the big double arm, and cut off one side. measure the arm with the stock one to see where you need to put the ball, and trim off some the excess as the one on the left side of the frame on the back will hit the canopy mount if left as is. A trick to get the balls in the holes without drilling is to use the screws that holds the servo in place, and screw them where the hole for the ball will be. Just keep screwing all the way till it's snug, then do at least 5-7 more turns to strip the plastic. You can then remove the screw and it should have enlarged the hole perfectly for the ball to get in there tight. If it's not enough, just put the screw in again and turn it more to get more plastic stripped. When installing the balls on the HS-65MG, you want to put them on the inside of the arm to have them perfectly perpendicular with the Swash plate. (Thanks to JohnnyV52 on helifreak.com for the tip!)
You might also have to reverse the servo channel on some of them to work as the stock.
Here's the settings I have for the DX6i:
Elevator - Reverse
Aileron - Normal
Pitch - Reverse
For the tail servo, I noticed that the stock one does a pretty good job. I replaced mine because I went with a better gyro and wanted a stronger tail servo. The D76T used on the tail is VERY quick, but has low torque, meaning that at high head speed, it might struggle to shift the angle of the tail blades where a slower but stronger servo would be better suited. Again, I would not replace the tail servo unless it isn't cutting it for you.
Here's what I recommend if upgrading your gyro:
Futaba S9257 Digital servo. It is plastic gears, but very durable, quick and lots of torque. (about 60$)
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