MARSOC is much more difficult to get into. You can enlist with Ranger in your Army contract (Option 40). Pass the 4 week RIP and boom you're a Ranger.
To be a MARSOC Operator you need at least 2 years as either (preferably) Rifleman or Recon man. The pipeline is so much longer than that of the Ranger pipeline.
Also, you must take note that as of right now, MARSOC operators (not all) will be tossed back into the Corps after 5ish years. Some are fortunate enough to stay MARSOC forever, but not all.
You can be a Ranger your whole career. You can also eventually try out for the big D if you so choose.
Army has a bigger enlistment bonus. Corps has a bigger re-enlistment bonus.
Also, though you may be a Ranger, you'll still be an 11b or whatever MOS you choose. There is no Ranger MOS. In the Corps, Recon is an MOS. I imagine that might help when it comes time for promotions and whatnot, seeing how there's less than 2,000 Recon Marines and probably tens of thousands of 11b Army Infantrymen.
MARSOC - long very hard road
Ranger - short but still hard road
It's your choice. They're both hardcore and badass.