I would try both of their demos. Personally I prefer Maitreya.

What Lynn said. Most of my friends advised Maitreya for ease of use and a broad range of clothing choices. I agree, but be prepared for frustrations with the alphas and masking layers.

If you have favourite designers and already have mesh clothing, definitely try out their Maitreya versions. And you may want a different shape for when you're in a mesh body.

Most designers are building for Maitreya first, then Slink second. Also, you'll need to rethink skins: you'll want an applier, if available, for your current skin.