Imo best to stay natural, interms of caffine. Its shown that caffine helps doms but id rather take bcaa's during training for that.
As said before its a bucketload cheaper to diy your own pre-workout supps if you really need. Unfortunetly caffine/any pre-w/o just doesnt effect me much. hell back in year 7 downed 4 espresso's at camp and slept like a baby. *sigh*
Id give jacked a try but they just dont have trial packs!