You actually posted that?
I didn't mean to be sarcastic, but merely concise...
If you were to suggest the best coin that should be merge-mined by the miners, which coin would that be?
Technically miners should be able to mine multiple merge mined coins at the same time, they don't have to choose only one.
But from a profitability perspective they'll have to check the market and see which coin has a higher value (or is being pumped at the time) that can give them higher fiat reward when sold.
From a utility perspective, the projects have to analyzed individually but if I wanted to choose only one I'd go with RootStock since it is a decent project and I believe side-chains are the better option that can satisfy everyone in this context (ie. provides additional revenue for the miner whilst has additional smart contract capabilities capable of creating
real tokens).