What I actually ended up going with was:
Set vs Charge(FX, p125)
- Set requires a Full Action (combined prepare & attack).
- Set weapon gains +4 AB (and -2 DR if not braced
against hard, unmoving surface, such as the ground) - Longer weapon strikes first, regardless of Initiative.
- Only Polearms may be set against Mounted attacks
So that this allows one to Set different weapons
I'm way late to weigh in on this topic, but for me to "set" a weapon against a charge, infantry or cavalry, etc, it needs to be touching the ground as well as pointing at the approaching enemy. So spears and other polearms are the obvious selection.
Always happy to tlak about things.

Yes, those are the obvious selection, and that is also implied as well with the second and the last bullet points, but being set is not limited to just polearms.
But if you aren't trying to do a real world simulator, not something I'd suggest with fantasy, I think I'd allow Tower Shields to be used as well. Obviously that's not something you can attack with, but it would be useful for helping to break charges, especially if in a shield wall or phalanx.
Historically speaking, such shields were often used in conjuction with spears, although usually in larger formations. With the formation creating a turtle formation or a hedgehog formation (if they had spears) against such mounted charge.
Smaller shields just can't be slammed to the ground and still be in the way of the attackers, and there are plenty of examples of real shields of that size having spikes on the bottom to help 'set' them.
I haven't read enough of the combat rules to figure out more than that yet, so take my comments with a grain or three of salt
No worries... I tried to make the Set vs. Charge rules both flexible and at least a little grounded, but also to allow it in other situations, such as an enemy closing on the character
For example, a character with a longsword versus a barbarian with a handaxe charging himon foot.
The longsword wielder can set against that charge (gets +4 AB, -2 DR, and attacks first since his weapon is larger).This is a valid usage of the Set rules and works well in that situation and fits with the generalized Set concept that is usually thought of as being spear versus mounted rider, and that works with these rules as well.

Thank you for your comments! I really do enjoy reading what folks think about the rules and how they are finding (liking or not) certain rules. Especially since feedback is what is needed to be able to improve the rules down the road...