Ok, I have shot the camp carbine, but not the Ruger. Here is what I have observed so far. Perhaps someone who has shot the Ruger can give you more info.
Marlin Camp Carbine -
Pro: Accurate, light, handy. You can use the same scope bases as the Marlin model 336/30 series rifles; they take hi-cap S&W 5900 series mags; genuine fun to shoot. Available in 9mm and .45 ACP.
Con: Out of production (NOT for political reasons, sales were slow, as per Marlin), not quite worth the $350 or so people want for them, Cannot use +P ammo safely. No .40 Auto version.
Ruger:
Pro: available with ghost ring sights, accurate (I am told), handy. Takes hi-cap Ruger pistol mags, apparently can handle +P ammo. Still in production.
Cons: Expensive ($450+), fairly heavy. Avilable in 9mm and .40 Auto only.
If Ruger makes a .45ACP version and ten round mags, I will get a Ruger.