As long as it's not Midwest Connect or Saver Service, pretty much any seat is good on Midwest Plus the B717 & MD83/88 series are somewhat similar in size, with 88-112 seats in the 2X2 format (not like comparing a 100-seat 717 with close to 200-seat 757).
By the way, just for comparison, I think a Midwest 717 Signature has 88 seats while Airtran 717 has 117 total seats-105 coach seats & 12 business class seats, which are almost the same as a Midwest coach seat!