DMR and/or OKWIN
For a mobile, Uniden BCD996P2 or BCD536HP or Whistler TRX2 if you're wanting to listen to Blanchard and Newcastle (they use DMR type radios).
Their portable equivalents are BCD325P2 and BCD436HP, and Whistler TRX1.
If you only care about listening to the Sheriff's office and other rural agencies that use the OKWIN system, then you have many more options. The models listed above should last you longer than other scanners if the OKWIN system ever upgrades to P25 Phase II.
If you don't care about Blanchard and Newcastle, you can get away with an older Uniden BCD996XT mobile or BCD396XT portable, or Whistler mobile WS1065, or portable WS1065. You will need a scanner that has trunking and digital, as Rosedale, Wayne and Purcell all have digital talkgroups on the OKWIN radio system. Again, the disadvantage to these radios is they may have a bit shorter useful life if P25 Phase II becomes popular in a few years.