I've tried more than a few and found that crank bros tool to pack a lot of punch into its form factor. For training rides, though, I might go with something a little more formidable:

http://www.jensonusa.com/store/produ...ulti+Tool.aspx

Pedros Tool with two tire irons that does it all, including tightening crank bolts if you forget to mind the torque specs while hastily throwing on your new crankset.