COB
has a softer light and higher brightness than SMD
SMD
has a small volume, light weight, and high density assembly
In my opinion, SMD is more popular than COB, and the usage is more widely.
so SMD is better than COB?
Welcome to BLF, LEDbucketR!
My impression is (without having done the research to back it up 
) that COB leds were not as efficient/cheap as distinct led-arrays, but they are catching up.
Philips' newest COB-leds have a very uniform illuminance over the entire surface, that would be optically very nice for an aspheric flashlight as well, if the voltage weren't 34V :-(
My understanding:
COB: More expensive, brighter, more likely to dim well, do not get as hot, last longer.
SMD: Cheaper, less efficient, more likely to dim incrementally or not well. Much more prevalent.
I opted for COB for about 150 spotlights in my house, cost was about 50-80% more.
If you are not limited on budget then go for COB 8)