The bar during scouting of course, the one that says "High" and is green on high potential players. Note that the bar is not correct until you actually scout him, after the first week of scouting, look at the talent bar again and look if it has moved up or down. After scouting a player for one week, you know the correct potential level. If a player there has a green bar, he's always at least a B, mostly A potential. If the bar is completely full, it's always A potential.
The draft grad has NOTHING to do with player potential or ratings. A player is NOT better just because he is rated in the first round. Actually, there's always a couple of intentional busts hidden in the first round, players with decent ratings that are only C potential. NEVER pick players because of the round they're set to go in, always look for the ones you scouted. The scouting and the skill hex combined never lie, if you got a player scouted with high potential and his skill hex looks great but he's a 5th round pick, then don't take anyone else, trade down if you want, take him in the 5th round, often enough the best players at a position are 3rd to 5th round picks.