Which premium are the Best
That depends on what you want to be close to. Each loop has advantages.
If you want to be close to the Settlement/Trail's End/Marina, then you'd want to be in 700 or 400.
If you want to be near Meadow recreation, then 900, 1200, 1300, 1000 and a part of 1400.
If you want seclusion, then 500, the middle of 800 or 1100 (although 1100 isn't as secluded as it was before they cleared all the foliage out).
All premium sites are about even. Some sites on 1400 can barely hold a pop-up, yet they try to squeak 40' motor homes on them. They tried to stick us in the last site on the left as you leave 1400 one time, and my little 32' MH would have filled the site. There was absolutely no room for my truck & utility trailer. There are also some sites in the middle of 1400 that they've actually put parking bumpers on to prevent people from backing straight into the canal. 1400, IMO, is for the most part a worthless loop (with the exception of about 5 sites). There are a couple of sites on 500 that are literally on top of each other. No way I'd accept those sites.
Basically, all loops are good. It just depends on what your priorities are.