Well lets test this:
Town Militia (England):
Attack: 2
Charge: 3
Defense: 2 (shield)
Bonus Attributes: Good Morale, Ability to Garrison (no upkeep)
Cost: 709
Upkeep: 117
Peasant (Reino de Espana):
Attack: 1
Charge: 2
Defense: 0 (no shield)
Abilities: None.
Cost: 532
Upkeep: 85
Custom Battle 1:
Town Militia 709 unit vs. Peasant 532 unit
Conclusion: Closer then I thought, 55 militia to 47 peasants (before the peasants broke). As a side note general killed close to 10 or so of the enemy. Peasant General died first, then moments later the militia dies as well.
Custom Battle 2:
Peasant Vs. Militia
Conclusion: Peasants lose this one as well with a 105 dead with the milita only losing 64. Peasant general falls first, but the militia one manages to stay standing.
Custom Battle 3:
Town Militia vs. Levy Spearmen.
Conclusion:Militia lose this round, with 94 dead while the levy have 76 fallen. Both generals fell with militia first then Levy right after.
Custom Battle 4:
Peasant vs. Levy Spearmen
Conclusion

easants lose with 105 left and Levy lost 61. Both Generals fell fairly close together with the peasants one dieing first. Alot closer then I thought!
Custom Battle 5:
3 Town Militia Vs. 4 Peasant (roughly the same cost)
Conclusion: Town Militia win. Town militia lose 144, while peasants lose 245 (no chase). Initial charge town militia actually lost more men, but it quickly even out and then peasants started losing badly. The formation for them was 2 wings and to mid (one behind the other). I met the wings 1 for 1 and had my general unit meet the mid, in the middle (basically straight charge as usual). After one unit broke then immediately did (maybe 1-2 seconds delay).
Custom Battle 6:
4 Peasants vs. 3 town militia
Conclusion

easants win, only losing 178 while militia lost 254. An odd occurance happened each of the 3 times I played this custom battle. The enemy would send 2 militia units to meet mine however its general unit would just hang back and occasionally charge and retreat, then rest for a bit/repeat. This never happened in any other battles so far which I find odd. Even when I charge it directly it attacks then runs away (sometimes far away). In any event if all three units did attack it would likely still be a victory for peasants though a lot closer I believe. I have saved one of the replays (the last one I did) if you want to see it.
Well thats enough custom battles for now. I'll admit I'm surprised at the way the peasants held up especially on 1v1 battles. I still believe, though, that without the free upkeep ability they are still a pretty useless unit in the grand scheme.