These guys are not similar in style at all but I'll compare 'em anyway.
LOPAD is a good album, but that's it. It's not all it's made out to be and Big L isn't the god lyricist he's made out to be. Yeah, he's clever and funny but at the end of the day, he doesn't branch out much from brag/punchline rap and light-horrorcore.
The DITC beats on his debut were very "of-the-time" and they don't stand out as being anything particularly special. I mean, compare Big L's best beats on his debut ("Put it On", "Da Graveyard", "No Endz, No Skinz") to Biggie's best on his debut. ("Me and My Bitch", "One More Chance", "Everyday Struggles") It's not even close, Biggie's beats had much more personality, more dynamics, and at the end of the day, were more interesting and memorable.
In terms of actual rapping, Biggie was also more versatile. His mic presence was monstrous. He told interesting and indelible stories, he could brag, and he was incredibly personable and likeable. (something that Big L was kind of lacking) Biggie's flow is hard to beat as well, look at his ever shifting spastic flow on "Hypnotize". When you've got a flow like that, you could rap the ABCs and still be interesting. Big could rap on hard beats or commercial beats ("Juicy") with ease and he did both well.
Overall, Big L was good (Personally, I think Mad Skillz was a better rapper and he kind of had L's style, check out his debut if you haven't) but I think his is the case of an enlarged legacy due to his death. Not many can do punchline/brag rap as good as L, but the dude seriously lacks versatility. Biggie on the other hand was something truly special and his two albums were classic.
So yeah, my vote goes to Biggie.