I thought I read that the HEMI's cylinder walls are not as strong as LS-engines. I know the first LS1s were pretty thin and later ones would accept a little larger honing, but I thought I remembered seeing that the 6.1s were thin. I think a lot of what's been posted is obvious regarding power and such so I won't beat a dead horse there. It's aluminum instead of heavier iron. I'm not sure of all the options for the HEMI, but you can get to 427 c.i. on an LS3 without resleeving (I've only seen sleeving options to get 426 on the HEMI, but again, I'm sure there are other options.) I believe the HEMI is more complex, at least in the ignition department. It's my understanding HEMIs needed double spark plugs in the past in order to burn off more the unburnt fuel in order to get past emissions; again, I don't know how reliable this is. LS-engines don't require this.As a MOPAR guy I'm sure you could give me insite there too
I know that LS-engines have pretty good rods and cranks but the early rod bolts were a liability. I've read about many LSXs (not the block, just generic for LS1, 2, 6, etc.) running 800 RWHP with stock cranks and a lot running with 600 RWHP with stock crank and rods and the LS3 has, largely, components from earlier LSX engines.
I think it's hard to argue, from the standpoint of what past posts already have, that the LS3 is just plain superior from the factory. When you start modding it, that might change, but I don't know enough about the HEMI to argue that...