If deciding on going to either GVAC Swap or the MCA Auction what would it be?
I think you'll get biased answers to that questions based on how strongly one person vs another affiliates with each club. I do believe both events are fundraisers for the clubs that enable them to hold speakers/events/etc throughout the year.
Thinking about this from your perspective, what kind of fish and/or equipment are you hoping to see?
From the MCA auction, you'll find a higher number of cichlids (and catfish + some plants) because the auction itself is restricted to only cichlids (plus a limited amount of catfish and plants per seller). You may find better prices here due to it being an auction. I'm not sure about this auction, but IIRC there's typically 600-850 bags in the auction. There is also a small priority fee to bump a bag to the front of the line if you're unable to stay all day for the entire auction.
At the GVAC swap you'll definitely see some cichlids, but there will also be a variety of other tropical fish and equipment. I'm not sure what the percentages of various types might be. Prices will be more fixed because it's a vendor-table-style event, though some may haggle with you if you want.
Personally, I'd recommended both if you can swing it. Then you'll experience each first hand and can make future decisions more accurately.