This shouldn't be in the theory forum. But what determines it (in approximately most important order):
But what determines it is cost, and what you need the capacitor to do (ie. better frequency response, accuracy, size, polarized/nonpolarized, pulse current capability etc).
At 48V, tantalum capacitors are pretty much ruled out and the only "affordable" ones left are electrolytics (cheap and large but poor frequency response, life, and temperature) and ceramics (better performance in pretty much everyway but smaller sizes and more expensive). Since you seem to be less than 10uF, I'd just go with ceramics in most places. 50V ceramics greater than 1uF or greater can get pretty expensive though so you might want to use electrolytics at those locations intead . It's basically down to cost.
I woudl use ceramics for C2 and C4. The only reason I would use electrolytics for C1 and C3 is because they have to be high voltage and larger size which gets a bit expensive with ceramics.