It's the middle of winter. my horse is on vacation until mid-February when I start legging him back up for shows so lets talk bits. I have two questions.
My horse collects pretty well and stops on his hind end in dry work but when we get to running the pattern he tends to want to rate on his forehand when going into the barrel. I don't want him to rate harder, just not on his forehand. So I want to be able to pick up and lift while encouraging him to not slow down so much.Which bit would you recommend to help with this? I also have to mention that his favorite mouthpiece is a 3 piece smooth with a chain link middle.

I also ride his in a snaffle for dry work and drills. Its just a regular oring, but sometimes I need to pick him up with both hands quite firmly to place him and he throws his head up(probably because of the two-piece nutcracker effect) should I buy a three peice with chain middle in a snaffle or not bother?

Can he do a simple roll back off the fence? I'd definitely make sure he's sharp there to get him engaging the hind in on and off the pattern. Its also helpful to do rollbacks at a pretty good speed (safely, of course), so he learns that when he's going a bit faster, he can still use his hind end.

He can perform pretty awesome rollbacks but we don't do them too often since he is 4. He also sits of his hind end when he stops and would probably slide if he had plates. He is also pretty good when we are loping the pattern, its just when I add more speed that he tends to want to dive instead of sit

If he's only 4 and performing well in dry work but not on the pattern, I'm tempted to say you're asking for too much speed to soon and it's a confidence issue more than a bit issue.

If he wants to dive, either you haven't taught him where he is suppose to be to set and then turn.  Also, be sure you are not diving too, be sure you are sitting where you want the horse to collect for the turn.

Is your horse coming 4 or coming 5 this year?

For myself personally, on such a young horse, if I am having problems with them getting heavy on the front end and/or throwing their norse in the air, I am going to look at my TRAINING before the bit. Yes, you do want to select a bit that the horse is most happy and responds the best with for that individual horse -- but on that same token, I want my horse well-trained enough to the point that they will be soft in the bridle no matter what I choose to put in their mouth.

Also, have you had his teeth checked?