Objective reasons for using Python or Ruby for a new REST Web API
Either will do a great job and you'll gain in other ways from learning something new. Why not spend as couple of days with each?  See how far you can get with a simple subset of the problem, then see how you feel. For bonus points report back here and answer your own question!
So this thread is definitely NOT a thread for why Python is better than Ruby or the inverse. Instead, this thread is for objective criticism on why you would pick one over the other to write a RESTful web API that's going to be used by many different clients, (mobile, web browsers, tablets etc).
Again, don't compare Ruby on Rails vs Django. This isn't a web app that's dependent on high level frameworks such as RoR or Django. I'd just like to hear why someone might choose one over the other to write a RESTful web API that they had to start tomorrow, completely from scratch and reasons they might go from one to another.
For me, syntax and language features are completely superfluous. The both offer an abundant amount of features and certainly both can achieve the same exact end goals. I think if someone flips a coin, it's a good enough reason to use one over the other. I'd just love to see what some of you web service experts who are very passionate about their work respond to why they would use one over the other in a very objective format.