I think it all depends on how you get around the course you play the most on. Would you be in a better position if you had a 3h for a few tee shots? Or, would a 4h come in handy more often? Would the 5h come into play more?
Tee shots are what I use hybrids for more than anything, especially the "power" hybrid LIke 4-5 times a round off the tee. Either 18* or 20* would probably fit the bill, as the 20* is equivalent in perforamnce to the 19* Srixon H85 I play now. The 18* is tempting for the extra firepower as a tee club - might even be too long though as it creeps up on the FW.
The 23* is more for long second shots, but truthfully the 4 spot in the bag is one that doesn't get used much.