I coach at a Y and love it. We only compete YMCA meets, but some will do USAG or AAU as well, if there isn't a strong YMCA league in your area. We do less hours than the private club down the street and continually make it clear our program is not designed to get your DD ready for college or the olympics, but to prepare your DD for life. We focus on the YMCA values of honesty, friendship, caring, responsibility, respect and faith. It makes for a great time!!!
We are competitive at the national YMCA competition and had girls qualify into the L8 finals, as well as take home a few first place AAs in L7 and L6. I like to think we run a great program, but have a different focus. We aren't focused on creating amazing athletes, but rather amazing young women. It just so happens that our coaches are experienced and educated, so we can also teach good gymnastics...which isn't necessarily the case in every Y (nor is it the case in every private club.)
I'm a major advocate for YMCA gymnastics. I grew up and competed in a private club and loved my experience there. It is what has driven me to coach and judge...however, the interaction I have with my girls now is completely different than my competitive experience...and my gymnasts are better than I ever was at gymnastics.
YMCA follows all USAG rules in terms of routines. However, individual networks, zones or districts are able to modify things based on what is best for their area. For example, in our area we do not have a deduction for coach on the floor, even at the optional levels. We also follow our state's High School rules for L9 bars. We were finding we had girls who could compete L9 on every event, except bars and they were being stuck at L8. So, our L9s use L8 special requirements and VPs, but start at a 9.7 and use L9 bonus and composition. Most YMCA zones or districts also have a "mandate" requirement, which is a set score that if a gymnast gets twice she is forced to move to the next competitive level for the next season. It keeps girls who are scoring 36s at L5 from competing L5 again the next year. However, there is a petition process, so if she was a great L5 but has fear issues at L6 and won't compete any of the salto skills, she can potentially still be allowed to be a L5 again. (This is a can of worms, it's not the best system, but its not the worst system...again...designed to not necessarily create the greatest gymnasts in the world, but to keep competition fun and accessible.)
So...in closing to my crazy long reply about something I'm super passionate about...YMCA gymnastics CAN be fantastic...it can also be unsafe and a little scary. Like a private club it really depends on your management, the philosophy towards gymnastics, and the coaches. There is one YMCA that I know placed girls at L10 USAG nationals this year, so it is possible, if you find the right Y...but most of us are just trying to make great people and if we win a medal along the way...good for us!