I'd like to see the M3 ENY lowered from the current value of 40. Maybe an ENY of 20 for the M3 to (literally) slow down the horde. We could still use the SdKfz 251 for troops and supplies, it would just be slower -- 33mph vs. 49mph.
If you do a search you'll see I've suggested this previously. It is more of an apple vs an orange comparison, really.
The thing is though the German SdKfz 251 has the "wurfkorper" rockets, which are awesome once you figure out the ranges, against towns. You can carry six of the rockets (285 lbs of dmg), which is good for a number of town buildings, and carry the 10 troops. Max speed is 33 mph.
The M3 when in transport mode can carry 10 troops and have the single .50 cal for defense. It can also take down at least 1 building with that same gun. Max speed is 49 mph (30% faster than the 251).
So, comparing transporting capabilities I say the M3 has the definite advantage that to speed. I'm not sure if it is because of the sloped armor or what but I tend to believe that the 251 survives longer against MG fire (armor thickness difference is negligible). Against cannons and ordnance there is no difference.
Now, bring in the 2nd role of each vehicle and the M3 takes the advantage: the 75mm cannon is far more efficient that the 251's 28cm rockets. If you can figure out the 251's Wurfkorper rockets you can carry 4 reloads an have fun in a town in a short manner
Basic stats:
Speed: M3 49mph vs 251 33mph
GV Supps: M3 (8) vs 251 (4)
Troops: M3 (10) vs 251 (10)
Base Supps: M3 (1) vs 251 (1)
Guns: M3 (1 .50 cal HMG) vs 251 (2 8mm MG's NOT linked), and (6) 28cm wurfkorper rockets
Armor: very similar
Ultimately, I do think the M3 is more valuable for its speed. The combat value of either is negligible. If the M3 ENY's were to be changed to 35 or even 30, it wouldn't change a thing in the game. So..... I don't see HTC changing this. Good luck.