Im looking to buy a new st croix spinning rod and am planning on purchasing the Avid. I currently have a st croix premeir in a medium fast action but am thinking about getting the avid in a medium heavy action. But im not sure. How much more heavier is the medium heavy? My father has a st croix tidemaster in a medium heavy, is that the same as the avids medium heavy? im not sure because my dads tidemaster is so much heavier than my premier. The tidemasters an inshore rod the avids a freshwater are the powers different? Also whats your opinions of the Avid?

The powers in the saltwater models are different than the freshwater models. St Croix's MH is heavier than most other company's. IMO, there is actually room for another model between the M and MH.

I have the 6'8" Med x-fast avid and it has plenty of power.  Overall, it is a great.  It might be the best bang for the buck rod I have ever used.   I have never had an issue with it and it handles just about anything I throw at it.

As S Havanec said, the salt water power ratings are different than the fresh water power ratings. The Avid series of rods are great rods and you can't go wrong with them. 

A St Croix Avid MH is functionally equivalent to most other manufacturer's heavy. I don't have, and have never held a Premier, so I can't compare.

I own the exact rod youre talking about getting.  I can say that it isnt as heavy as my daiwa heavy action or my cabelas heavy rod but it stacks up to a dobyns 5 power rod quite well.  I am using my 7' avid spinning MH-F to compare to my dobyns 735c MH-XF

I have a Med=heavy st-croix avid and Its a great stick, however I feelthe medium action can handle most lure applications up to the 3/8oz -1/2oz class...Id go with the medium-heavy, oinly if your gonna be doig heavy spinnerbaiting or frogging with it.