I’m looking at the st.croix legend tournament and am trying to decide between the medium fast or medium heavy moderate fast, what are the main differences? Thanks 

As a rule, the MH has more power than the M, and the fast action bends closer to the tip than the moderate. 
 

A good question is what do you plan to fish with it? Crankbaits? Texas rigs? Spinnerbaits? 
 

Let everyone know what you plan on using the rod for and you’ll get all the answers you need. 

I will mainly be fishing t rigs, probably 1/8 to 1/4 mainly 3/16 and 14 pound Fluoro with 5 inch senkos and fat aces. I’m also looking for a good cranking rod but it would be mainly for deeper divers ( 15 - 22 ft. 

I'll let others address the crankbaits, as I am not a big crankbait angler. But I fish the TR a lot, and I prefer a MH/F rod for that. I like the added power when setting a 3/0 or 4/0 EWG hook. 

Are you limited to one rod? Personally I would get a MH/F if you mostly use texas rigs. If you want to crank well I would recommend getting another rod, for reaction a cheaper rod will do IMO as liong as the action is right