For me it boils down to this; the basics(fs, bbbj) are usually a given with SP's and they cost less BUT they are generally less attractive.
What are you talking about, no they are not. For a hh SP's cost 160 to 200(for VIP) for the hr 250 to 300(VIP) and you know for sure that is how much they cost. For the same services an MPA's at seduction will cost 240 to 290 for a hh and 340 to 390 for the hr, possible more depending on her discretion. 140hh/240hr for the room fee plus 100 to 150(or more) for the tip to get extras, the bj is often covered only for mpa while bbbj is practically a given with sp's no questions asked.
Though yes you get a couple Xtra minutes at the spa since shower time doesn't count for mpas but does with sp's. If one just wants a erotic massage/body side obviously just go see an mpa and it will be cheaper but imo that's not what the op is talking about.
But yeah it is nice to be able to see the girls first at the spa before booking them. Though the better girls are often booked up so it takes some luck to catch them. Also one sp agency- Sassy Angels does allow for walk outs if your not satisfied with the girl, but their girls are much thicker in general.
Few other things; Some of the more popular sp require prebooking days ahead of time, most mp's can be booked same day.
Also, spas only have a massage table, sp's usually use a condo or hotel room with a large bed for the action.
Spa's are better for walking in option and are open much later so they're best for late night options while most agencies don't operate past 10 or 11 cept for sfto which sometimes has girls working till 1 or 2. But most agency girls are usually fully booked hours ahead of their end time.
Best be to open an account on the red board(terb). Lots of reviews about sp's including Latinas there.