I think Smooth kinda sums it up, as well as what Huseby said.
What really matters is how you plan to use it. If you're looking at using this build a lot in Strategus and Team-Settings, then focus more on Strength. If you find that you are going to be soloing a lot without backup or minimal backup, put a little more agility in it. Personally I would definitely try to keep your strength above 21, just so you still have that kill-power.
You're really going to have to learn the different techniques associated with each possible build though, so be prepared to have your ass handed to you for a few days until you learn it. The best technique for a high agility build I've found is to either Strike, then immediately run facing away from them then turn around and attack again, almost like you're doing a Figure-8. It contains them and sometimes will confuse them. The next step would be to engage, swipe past, prepare your attack, jump, release, and spin it into them.
You'll find a lot of fun things you can do with it, but to be clear as to why I choose higher strength...
You have a 1-directional weapon here that you plan to use. The chances of you successfully and time-efficiently striking 3-4 blows on a 15/24 build without assistance are minimal. I like to capitalize on the amount of output in damage I can do with those one or two chances I may get to land on them.I would also read Caita's guide to Pike and Long Spear usage. He really put together a great collaborative guide on how to properly use these types of spears and you may be surprised to find something in there that will help you a LOT.
http://forum.c-rpg.net/index.php/topic,25312.0.html