Unless there's an innings limit, I always like to go pitcher-heavy on my bench in a head-to-head league. Many teams have the same off days, so often your bench hitters will be off the same days as your starters so you can't guarantee being able to grab extra stats that way. But as long as all your starters aren't scheduled for the same day, you can rotate them in when they're scheduled to go and maximize your shot at wins, Ks, etc. (and you can always keep them on your bench if there's a bad matchup and you don't want to risk your ERA, WHIP, etc.). Also, you might want to carry some extra relievers as your league counts both saves and holds.
If you do keep any bench hitters, try for players that are eligible at several positions (a guy like Desi Relaford is a great guy to have on your bench because he can fill in for a bunch of different spots) or go for a backup catcher because catchers always have more days off to rest (it's tough to know when they'll be off sometimes, but you can usually bank on a day game after a night game or watch if a certain starter has a personal catcher, etc.) or get a guy that plays the same position as someone on your roster with an injury history (an OF if you drafted Jenkins or Griffey, etc.). Overall, with five bench spots, I'd leave at least three (if not four) for pitchers, with the 1-2 hitters fitting into one of the categories mentioned above.
Of course, these are general rules of thumb. It all depends on who is available in your league. Don't hold onto three extra mediocre pitchers just to have extra pitching if there are great hitters still available. But chances are, you'll be able to find pitching on the waiver wire easier than finding hitting, and surprising pitchers generally crop up more often as the season wears on than do surprising hitters, so keep an active eye on your waiver wire and don't be afraid to shake up that bench when necessary. Hope that helps (unless you're in one of my leagues, in which case please ignore all of the above LOL).
"I'm telling ya, he jumped us. Gloves off, stick down, no warning. He challenged the Chiefs. Called us names. But Dave was there."
"Dave's a killer."
"Yeah, Dave's a killer."
"Dave's a mess."