Sherr, I buy a pineapple every week from the supermarket and just pick the biggest. I can honestly say Ive never had one that isn't ripe, I've never tested any by pulling leaves off, or squeezing or sniffing.
My feeling, rightly or wrongly, is that by the time they reach the shops here they're all ripe enough to eat straight away.
I cut the top and bottom off, stand it on end and slice the peel off, then quarter it longways. The hard core is then easy remove from each quarter, and the juicy flesh can be chopped into chunks.