I'd go with OEM. A common problem with after-market is squeeling
and I imagine the harder brake compund Midas might use (for long
pad life) could be more prone to squeeling. Also, harder brake
compounds probably don't stop the car as fast as softer pads
(for street use).

Also, you gotta think Volvo did a lot more research on brake performance
on their cars then Midas did and came up with a good compromise between
performance, life, costs and other factors.

In case you have any do-it-yourself inclinations: The brakes are not
at all hard to service. Parts are reasonable at discounters like
www.volvoparts.com.

You do need to keep an eye on the OEM pads. They go about 30K between
replacement (front) and they do not squeek, chirp, or anything like
that when they are worn down (as some pads do). You have to visually
check them.