THAC0 is tolerable in precisely one situation: the GM tells you your opponent's AC. Then, you roll your d20, add your modifiers and the AC you've been given, and if you match your THAC0 or better, then you've hit.
Example 1: THAC0 of 15, AC 3, +2 to hit. Roll a d20, get 13. So, 13 (d20 roll) +3 (AC) +2 = 17 (>THAC0). Enough to hit.
Example 2: THAC0 of 7, AC -5, +1 to hit. Roll a d20, get 8. So, 8 (d20 roll) -5 (AC) +1 = 4 (<THAC0). Not enough to hit.
Note how this arrangement removes the requirement for any subtraction (unless the AC is negative, but it's not too difficult to apply here). Also, except for the d20, it's pretty much all single digit numbers, which is a slight advantage. Just make sure to apply bonuses to the opponent's AC correctly.
That said, I still prefer Ascending AC and Attack Bonus, but it's the one way that THAC0 becomes usable. If your GM refuses to tell you the opponent's AC, then I suggest you do what we did when we played 2e: use the THAC0 to reconstruct a 1e style to hit table, and screw the stupid mechanic.