Oh, we all know Shinichi would have certainly figured out Light was Kira on day one!
They're both very similar detectives, however the way they handle cases are much different. I would argue that Shinichi is much more aggressive — or at least, he's put into far more dangerous situations that make him appear to be. Shinichi will hop into the fray regardless of the dangers, driven to find that one single truth by all means necessary. L would just as well have send someone else as his investigator to gather whatever information he needed.
Therefore, I believe L is more likely to play it safe. Shinichi is more impulsive, though he has his wits to keep him safe.
L, on the other hand, is more manipulative, almost like a "mind detective". Instead of solely physical evidence, he pays more attention to the demeanor of his suspect and their tone. At least in the Kira Case.
Quite frankly, I bet they would make a great team. L, with all of his resources and influence, would easily be able to pinpoint the location(s) of the Black Organization hideout(s) and where Kira is located.
Meanwhile, Shinichi could fill in the gaps of detaining them. Undoubtedly with all of the sophisticated and complex ways to murder individuals he has deciphered, laying some sort of trap or acquiring the physical evidence of their crimes would be plausible for him.
Besides, Kira couldn't kill Shinichi. After all, his persona of "Conan Edogawa" doesn't really exist!
In conclusion, I'll end my rambling with this — Shinichi is more of a "field operative", whereas L has more resource information to rely on and therefore more of a "behind the scenes" guy.