All are good servo's I have used the 3550 the 3650 and the 94145 - the 94145 and 3650 are the fastest (and even better wtih a radio like the JRZ1 that has high speed mode) the biggest difference is the 3650 has more tourque which I feel makes a bit of a difference - of all three I got rid of my 3550's because the 3650 out performs it - but I keep the 94145 because it is really the fastest servo .07 compared to .09 with the 3650 - but who can tell .02 sec difference anyway.............I run Jrservos most of the time because I'm using a JRZ1 radio . If I had an Airtronics radio I'd run Airtonics serv's - KO same ect. It's all good................