Only you can really place value on what matters to you most...
But as a DL Diamond who's flown Frontier many times and used the MKE airport plenty, I think you'll be pleased with F9. The baggage fees are an annoyance and I don't blame you there...as a previous poster noted you might want to check the Classic fare price; I've found sometimes it's not a heck of a lot more and you get free bags and other perks.
As for onboard, I think you'll really enjoy Frontier. It's not first class but the seats are 18 inches wide (vs 17), legroom is pretty good, you get live TV and the flight attendants have always been among the best I've had.
Frontier is a good airline and if I lived in DEN, I'd fly them a heck of a lot more...