I primarily only buy both HC & TPB color reprints, i.e. Masterworks, Omnibuses, Marvel Classics, etc.

I usually won't buy b&w reprints unless the material being reprinted was originally in b&w, i.e. the excellent DH Savage Sword of Conan phone-book reprints.  Though the Marvel Essential volumes are definitely better than nothing, I feel that my enjoyment of the material isn't the same unless I'm seeing it as it was originally presented; the Spider-man Essential reprints are a great example of this, since the colors in the original comics really made the stories "pop", and seeing these same issues in b&w is somewhat bland.  That being said, I am very tempted by the recent (or forthcoming?!) Web of Spider Man #1 Essential volume - I have fond memories of reading these issues back in the day, and especially like the cover of #1, with art by Charles Vess - also, this material has never been reprinted anywhere.

Ultimately, however, it's just a matter of personal preference - buy what you want and/or can afford.