im looking at buying one of the following head to put into my rig:
ashdown Mag 300H
hartke HA2500
warwick ProFet 3.2,
marshall MB450H
Laney RB9
with one or multiple ampeg B-115E cabs. i was wondering wich head will provide me with better tone for playing metal & classic/souther rock & if they would be loud enough to use live.
Try the marshall theyre alrite.
I personally would say get an Ampeg head to match the cab. they do some entry prices solid state heads i believe, they sound awesome.

You could try the Ashdown, i also have an EB12 and i tried that head in the shop and it sounded great.

Ide go for the Ashdown personally!
The Official "Rockin' Roadie"

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-Various pedals
Generally the Hartke set up will work. You sure you want 15's? That is a lot of bottom for the music you are playing. Four ten speaker cabs would probably work better. Just suggesting. Depends on each individual.
What I'm Trying to say here is that in my experience if you are playing in a band through a p.a. the bottom is picked up by the p.a. Your bass rig is basically a monitor. So you want some thing that cuts through on stage for other bandmates to hear. If you are playing with the instruments "raw" and vocals through the p.a. you might want something more bottom. But you still need to cut through the mix.
Two things to consider E.Q. and volume. Turning certain e.q. knobs can make you appear to be louder than you are. Of course The pure wattage of an amp can make you loud.