Stock power, I think you'd be fine with any type. I tend to prefer fiberglass as they don't bend/kink, but they do split if abused too mu
A good rule of thumb is: The longer (physically) antenna you can run, and the higher up you can mount it, and the closest to the centerline, the better it will perform. (ie: mid roof is usually best, but it's a horrible location for offroading)
You already know this -- a proper length whip is your best option with stock power. (I would run it off a rear bumper before I took the chance of beating up my hood & windshield, depending on how off road you get)
I've never really seen these helical perform that much better; some swear by em, some say they are a gimmick, I think they are just too big for a mobile install...
No matter what you get -- tuning your antenna will help a lot; I hate seeing people just buy an antenna and slapping it on and then blame something for poor performance, when it just needs to be tuned/trimmed/etc.
If you do go fiberglass, keep a spare in your toolbox, they can get brittle and split if abused and they can't just be glued back together (or brazed back together as you can with an aluminum tube type) A whip can kink, and that will kill its performance. I have found firestiks good (I would suggest their lighter weight one as they are more flexible and take more abuse, especially since you're ampless)
Post back what you go with & how you like it.