The best ply grade that's commonly available is B/BB, the "B" face may have one or two tiny natural blemishes but it won't have any plugs. The "BB" face will almost certainly have several plugs so that goes on the back or the inside. Even B/BB allows a few voids within the grading system.
Next down is S/BB. The "S" face will have plugs, but a lot fewer than the "BB" face and often they're better executed, i.e. with wiggly edges so they blend better rather than rugby ball shapes. You used to be able to get a slightly better version called S+/BB, with even fewer plugs, but I haven't seen any for years.
All of the faces on these higher quality grades should come sanded smooth.
The problem with ply is the grading is only part of the story. All ply has thickness variations, but with some manufacturers the variation is more extreme and it can even vary by a few tenths within an individual sheet. I also had a sheet recently that was actually thicker than the nominal size, something I'd never seen before. Another issue is how well it's been stored in the distribution pipeline. Good suppliers store it flat, bad suppliers lean it against a damp wall for weeks on end until it's like a model of a skateboarding park. A decent supplier will also give you a choice of long or short grain configuration.
If you've got deep pockets there's also speciality ply. For example there's a German company that manufactures Beech and Poplar ply, it's within a few thou of nominal and has zero voids or defects. It's been a while since I bought any but I recall it was at least twice the price of B/BB.
Another trick is to buy speciality model making ply, it's only available up to about 3mm thick but it's flawless, you can then make up your own thicker ply by laminating this stuff together.
