The University of Central Oklahoma in Edmond has 4 Panhellenic groups: AGD, AXD, DZ and SK. From what I understand, recruitment is not cut throat. Formal recruitment prior to start of school. There seems to be an emphasis on panhellenic cooperation at the school as there are yearly panhellenic seminars for all new members and returning members to foster unity and communication.
My knowledge of OCU is too old to be of much help, but my best friend was a Gamma Phi there and absolutely loved greek life at OCU. Sororities there are: Alpha Phi, Gamma Phi and Alpha Chi Omega.
Northeatern State: fun fact: Carrie Underwood was a Tri Sigma at Northeastern State at Talequah. If you read the rush thread that someone else posted about Northeastern, it sounds as if recruitment there is wonderful with 4 great strong groups, Tri Sig, ASA AOII and DZ.
I'm trying to think of other smaller schools in OK-- OBU doesn't allow national sororities, Southeastern in Durant has Tri Sigma and AST, so don't know if having only two sororities makes it very competitive, or very relaxed!
Good luck with where ever you go, and post your story later.