For the LA series smallblocks, Mopar changed the compresison ratio mostly with combustion chamber size and design, but a little with piston height. In my opinion, the most desireable stock Mopar smallblock heads are the late 80s/early 90s swirl port closed chamber heads (302 casting for 318s, 308 for 360s). These heads have a closed chamber small volume combustion chamber with swirl port design. Dyno tests have shown a 25 hp gain just by bolting on a stock set of these heads. I have a set of the 302 heds I am going to install on the 318 in my 82 Ramcharger.
You can mill the heads or deck the block to increase compression, but too much milling and/or decking requires modification to the intake manifold and valve train. The easier way to increase compression (outside of switching to a head with a smaller combustion chamber) is to use different pistons with a wrist pin farther away from the crown of the piston.
But if all you are wanting to deal with is a head swap, the late 80s/90s swirl port heads are the best LA head design done by Chrysler. As Hasan Ben Sober noted, these heads have a reputation for crackign, so it is best to either buy a rebuilt pair or at least have the ones you want to use checked out. But it is often just as expensive to rebuild a set of heads as it is to buy a new set of rebuilt heads, so unless you are doing custom porting work on a race motor, you should definitely shop around and research the cost of rebuilding what you have vs. buying new.
Good info here: http://www.hotrod.com/articles/mopp-0607-mopar-cylinder-head/