As Mechans noted, it depends on your room size and listening levels and music choices. As far as the speaker is concerned, its sensitivity is a good spec to consider -- higher sensitivity needs less power.
The Studio 10 is a little larger than the Signature S1 yet the S1 is one dB more efficient. The key difference between the two to me, is that the S1 is a sealed design. That means its bass will roll off with a 2nd order slope, where as, the ported Studio 10 will roll off with a 4th order slope. This also tends to affect group delay -- sealed designs have better (lower) group delay.
Sadly, you don't see many acoustic suspension designs these days. It doesn't matter the manufacturer, small speakers cannot make clean bass and shouldn't try. Adding a port to extend the bass response just causes problems. Properly integrate a sealed sub to extend the bass response seems a wiser approach to me.
With that in mind, there's always NHT and more recently Wharfedale's Jade series has some sealed (and almost sealed) models. Look at the Jade 1 and Jade 3.