I own them both.
The LCP is very reliable for a pocket pistol of its size. I have not found it to be finicky. 4 malfs in 1500 rounds. It may not run EVERY load, but it should be good.
Main advantage of the LCP is extremely small size, as mentioned. I have found I can carry the LCR revolver in a pocket, but it works best if I don't put it in a holster because with a holster it's simply too bulky. Weight is not an issue with the LCR.
I am disappointed in my LCR mainly because I believed the Web hype that it's much more comfortable to shoot than a Smith Airweight. It isn't. I find the recoil harsh except for the target wadcutters that some recommend. Fed Personal Defense is tolerable, as is Aguila 158 gr. JHP. Hornady is harsher, so are FBI loads, and don't even think of buying Buffalo Bore.
Accuracy, probably a bit easier to shoot the LCR because it has sights. The LCP really doesn't, though with practice it's accurate about to 7 yards, which is about the maximum distance I would deploy either of these guns.
LCP has a heavy trigger which smooths over time. There is some recoil pain which is lessened by adding magazine baseplate extensions from Ruger or Pearce Grip (these are also crucial for control) and a Pachmayr Tactical Grip Glove slip on grip. With these add-ons, the LCP is noticeably more comfortable to shoot than the LCR. Neither is a pleasant range gun, however.