The best mowers are not the best loaders, and visa-versa. Best mowing tractor is a JD X749. It's all-wheel steel, all wheel drive, in a very short wheelbase, making it almost as manueverable as a zero turn and fitting where most CUTs/SCUTs can't. But, it can't be had with a loader. The X748 gives up AWS but then supports a small loader (similar to a small BX). These are awesome mowers, snow movers (plow or blow), tillers, and general garden tools, but not much for real loader work. Easy on the lawn, easy to store, easy to tow. Extremely reliable. Outstandingly engineered for easy maintenance and attachment design.
ZTs are the fastest, assuming your lanscape lends itself to using one: flat, smooth. But, really only good for mowing. Tractors are more versatile; can do many other things.
A lot of good options, but no perfect do-it-all-very-well machine.
Best compromise with a mower lean: BX's, JD2320/2520, GCs, B-series botas, smallest NH, LS, cub cadet diesels, TYM T233 or T273
Best loaders that can mow: Kioti CKs, Bobcat CTs, small Mahindras, TYM T293, JD 2520, 2720, and 3000 series, bota grand-Ls, NH boomers with supersteer.
I don't like using a loader with the mower deck underneath. So, mower/loader on/off are important to me. In this area, no one beats JD, especially in the 2000/3000 series.
The new JD1026R might be worth checking out too, if they ever release it to market.
Best buy: Kioti/Bobcat, but they are heavy.