The major differences between the factions are their starting locations: the english get a pretty secure base of operations (once the scots are taken care of) while the french have got it pretty tough, potentially having the HRE, milan, denmark and spain as adversaries on top of the english.

As has been noted, the longbow's stakes make a lot of difference - effectively neutering the french cavalry advantage in a defensive battle. And english get longbows practically from the word go, so the two factions actually play very differently in the field, and complement each other really nicely.

And i just want to agree with the comment about the armoured swordsmen upkeep. It really makes a very big difference to the size of the standing army you can field when their support costs are 2/3 that of DFK/DCKs.

Having said that, if as the french you manage to push the english off of the mainland early on, the AI will find it very hard to regain a foothold there.