Some folks would say STA=HP so put it all in STA. It used to be that STA was the hardest to raise by gear. However, there is more STA gear out there now and the rules on exhaustion have been changed so its not as critical as it once was.

DEX helps a little with preventing missed notes, offensive skill ups, and weapon procs. A good DEX doesn't hurt.

STR is nice since bards are a plate armor wearing class and plate armor can get heavy. It also will affect your damage output a little.

CHA is important. If your Lull song gets resisted your CHA score will determine if the mob will aggro on you or not. The boost you get with NPC merchants is useful, too.

If you try tradeskills STR is usefull for smithing. Dex is good for fletching (and possibly jewelry crafting). CHA is good since it will lower your cost for supplies from NPC vendors.