[jarel]

If you don't care about Gambit's C integration, go with Racket, it's very beginner friendly and has lots of libraries.

Or:

If you don't care for Rackets IDE, go with Guile, it's the official GNU extension language.

TL;DR find a Scheme implementation that is good at what you need and use it.

[rohshall]

Apart from Racket, Chicken Scheme is the most active Scheme and it has a lot of libraries (eggs as they call it) from OS interface to amazon web services and web frameworks.