Commit covered most of this.
Do you get to choose if you do company or contract flying? If so is it on a month to month basis?
We bid early in the month for contract "lines" and can also bid for our 9 "hard" days off. If you are awarded a contract "line" your days off are set by the awarded line. If you are not awarded a contract line then you awarded "hard" days off (mostly based on seniority) and the company adds the additional 3 (or more) days off of their choosing.
Both processes are done every 28-day bid period.
What makes MIA not commutable? I heard they did lots of day turns of of Miami, but don't know if that is still current.
It's not really any less commutable than working for Envoy or AA (or now Spirit) out of MIA. If your bid works out, you could be off and at home for 12+ days in a row.
The "yuck factor" is that most of the MIA flying is late night and/or early morning and they can also mix in MIA reserve days without much regard to seniority.
The non-commutable part is that you're not getting the benefit of having a paid hotel for 3 nights per 4-day trip like you'd have with most PAX carriers. You'll be out the cash for hotels or a crash pad 16-19 days a bid period depending on how those additional days off are placed by the company. Doing the MIA stuff as a commuter is pretty similar to being on short call reserve.