I don't remember how much Health you have as a level 25, but I think padres back beach is a good place to start for any weapon really. If your about to die you just run into one of the houses and there are places to reload things like grenades and such.
Outcast is where I mainly leveled mine I think. There are gypsies on both sides of the island that helped out a lot. Another pirate to heal you is also a good idea. If you get a friend who hasn't mastered their voodoo doll than they will get rep too as you level. I helped a friend gain almost a full level once, just for healing me!
It really all depends on how much your pirate can withstand, if there are gypsies or a quick escape anywhere close by, and what lvl enemies will give you max rep. Try to figure that out first. You don't want to be killing a level 39 if a lvl 29 will give you max rep as well. Hope that wasn't too confusing.. my mind tends to run in a million different directions when I type lol...
This thread also might be some use to you:
http://www.piratesonlineforums.com/f...ht=level+guide