I would personally guess Spirit because of their carribean presence. And with Jetblue going head to head with Spirit out of FLL, I believe Spirit is going to be in a lot of trouble. All of Spirits planes are leased. So it would be easy to replace them with 737's. Spirit will have 32 planes as of next summer which would be a growth of aroun 6-7% for SW. Spirit only has a little over 100 million in cash and investments. So I believe the asking price would be around the same as Frontier. If they already bid on an all airbus carrier, they could do it again. And it is the only LCC I know of that is almost all international flying.

Sun Country could happen. They are in bankruptcy. But with 8 planes, it would probably just be a way to buy some cheap 737's.

Just my 2 cents.