mid tier

First off, these are the middle tiers...
Upper Middle:
FH, ΑΤΩ, ΛΧΑ, ΣΦΕ, ΣΠ
Lower Middle:
ΠΚΑ, ΠΚΦ, ΣΤΓ, ΦΚΤ, ΔΣΦ, ΔΧ

The Upper Mid tier fraternities are usually the fallback houses for those that weren't able to get a bid the top tier fraternities. Even though they aren't on the top, they're still pretty good, having at least a decent influence around campus and being known by most students. They're classified under the top tiers because they fall short in at least 2/3 of these areas: recruitment, top sorority relations, and social popularity.

The Lower Mid tier fraternities typically struggle more in recruitment and socially than the upper mid tiers. Because of lower their rush attendance rates, they typically give bids to anyone they can in order to get decent numbers. This results in a tighter budget than the large fraternities deal with, so they can't throw many big parties. However, the smaller size usually makes these fraternities some of the closest brotherhoods on campus, which can be very appealing for some people.

That as accurate as you'll get on here without me individually describing each fraternity. Hope this helps!