If you're going to be fishing B-n-T tourney's I'd recommend the biggest livewell you can make fit. Storage bins can be better than a cooler as they are lighter with more internal space for the fish and you will be circulating water from where your fishing so the insulation of a cooler has no benefit. A good rule of thumb is can you fit a 10# with 4 others over 2#. Most of our tourneys are won with under 15# for a daily limit, but occasionally they will go over 20#.
Tight lines,
Wade