You don't really say what the problem is for you to warrant changing a bit...
This question has been done to death on every horse forum.
Whilst it is obviously in yours and your horse's interests to find the best bit, please bear in mind that 9 times out of 10, it's not the bit which is the problem, it's the rider.
Bits go in and out of fashion. In the 80's people had thick, fat bits. Fat snaffles, fat fulmers, fat happy-mouth bits etc....
The current "craze" (and I speak only for classical riding only as I don't know anything about Western) are the Myler bits.
Bit manufacturers promise you that if you use their bit on your horse you will get amazing results. Whether it's getting your horse on the bit, or flexing or control when jumping etc... The latest trendy bit assures you that it will work miracles.
If the bit in your horse's mouth appears to be too close to his teeth and there are not enough wrinkles in the corners of his mouth, then perhaps a simple adjustment would suffice.
I hope that you find the answer, because with all the hundreds of bits around, it is very confusing, even for the most knowledgeable expert!