You'd have to factor in seasons played, general ability, the types of teams played for and how much they tested their value on the market. It'd probably be someone on the most games played leaderboard.
Looking at the All-Time Player Records section of the media guide, there seem to be a few marks that might not be broken for a long time, if at all.
No active player is within about 500 blocks of Dwight's mark of 1,050. Gaze has a 5,000 point lead over Loggins and is over 9,000 clear of even the fifth best. Gaze's assist mark is about 1,000 clear of Heal, and he's about 500 fouls ahead of any active player.
On the boards, Bradtke's numbers are miles clear of any actives while the same is true for D-Mac in steals and Gaze in turnovers.
In fact, the only record in this class that might be challenged is Gaze's total for threes made which stands at 1,826. Heal was at 1,512 before this season, and makes about 100 or so per season - if he can convince the Blaze to keep him employed for a few more years and giving him similar minutes, he might get there.