I would be just a little bit more selective about regionals than "fastest upgrade". Some of them are pretty toxic work environments, and those are potentially more likely to get sideways if you do more than one weekend/month of mil, which would be a problem for you. You would win that battle, but you don't need the aggravation.
The good news is that upgrades are fast almost everywhere right now, so shoot for a regional with a junior pilot domicile very near your guard base (or co-located with if that's possible).
Do your homework before selecting any regional. Most of them will work you to the bone these days (pilot shortage), but some of them have truly toxic cultures... no point in subjecting yourself to that unnecessarily. Also ensure you understand their training program... some of them just throw ten candidates on the wall and hope a few stick. There's a lot of luck and personality involved in that sort of program, so no amount of work ethic or fighter pilot kung-fu will guarantee success (you don't need an FAA pink slip on your record obviously).