Sounds like the pool would be the deal breaker for staying at Olive 8.
Benefits of the Grand Hyatt is relatively easy executive suite upgrade for diamonds or at least the bigger corner room / oversize tubs / view. Nice and empty fitness center. They also have a Regency Club with offerings that are very ordinary but the club itself looks nice. Usually run by one overworked and probably underpaid individual.
Benefits of Olive 8 is large pool and nice changing room with steam / sauna (no lockers) and of course generous breakfest benefit for diamonds. Upgrades for diamond memebers is fairly hard here because they always seem to run pretty full on weekends and they work hard to sell the upgrades in advance to guests willing to pay the upgrade fee. So expect an ordinary room.
Both Happy Hours at Olive 8's "Urbane" and Grand's Ruth Chris are worth a try even on the same night.
Along with good food specials Urbane has decent draft specials and Ruth Chris has amazing prices on Martini, Lemon Drop, etc.