I've become a "bit collector" or so I thought until I started checking thru what I had to switch some out. Most of mine turn out to be the same or similar - basic snaffles. Where they are different is in the rings - some are various riding styles and others are driving style. I have full cheek, eggbut, round and d ring ring riding snaffles - some fairly thick diameter and others somewhat smaller. Mostly from 3.75 - 4.25 " wide. Also, I started out with "cheap" plated bits - the plating wears off and they become burred and rusty.
When I started driving - I used what I had BUT do find that that can pull a bit thru their mouths... I really like the 1/2 cheek driving bits - and now have some that are basic snaffles and some that are the french links w/ either just a copper "bean" or the whole mouthpiece is copper. The ponies I'm currently working those in are VERY happy with them...
Now, I have an issue with a 2 yr old filly. One that I'm not familiar with - almost from the very beginning of starting her (Dec 2012) - she's tucked her head well behind the verticle - rather than balancing by traveling with her head somewhat foreward and nose stuck out... She's in a very small diameter mini size snaffle (one joint)... I got these specifically for my smaller shetlands as some were having such a problem with the "thicker" bits. When I checked w/ a pro trainer (3 actually) - they all recommended going to thicker diameter bit, &/or wrapping it, or maybe even a rubber or leather bit - straight bar rather than snaffle. When going thru my bits, discovered I don't have any straight bar (mullen type) bits - but we tried a thicker diameter snaffle and worked on driving her forward and ... she's better. SOOO think that the tiny diameter was the problem. She does need to learn to reach forward and carry the bit, though. Time and experience will have to happen next, she's still an immature baby as well.
Rhonda - I agree with others. If your bit works for her - no reason to replace it UNLESS it's one of the less expensive, plated ones that peels, burrs and rusts. But then I'd replace it mainly with one that is the same - just made out of better materials, not a completely different bit.
I've often "eyed" the Myler bits - but why should I spend $125 - 175 (or more) on a bit when they go perfectly fine in a $20 - 40 bit? Now, as I advance in my driving and get into dressage work and showing in the ring in different disciplines, that may change. Then we will go to other bits - as needed &/or required by the level or the discipline... In some ways - it's so nice to have the choices we now have with our little equine - but it's definitely more confusing and causes us to spend lots more, LOL!