Follow the hours/month. That will be 135 or cfi. Maybe jump or banner tow

seaplane/tailwheel: NO

I wound up going the CFI route in 2019 and logged as much as I could from it. When Covid hit, I was short of ATP mins by about 250 hours. The hours were hard to come by, but even then, I continued to fly them—albeit with less demand. Eventually, when I got them and we turned the calendar to 2021, the Regionals started calling.

I know a few guys who left instruction (temporarily, during Covid) to pickup work outside of the industry. It gave them a paycheck, but their flight time took a hit and, as a result, couldn't grow as much. Some of those guys are still chipping away at their ATP mins now and have yet to get calls from the Regionals to the best of my knowledge. (Although the calls will certainly come soon enough.)

My point: do whatever you can to consistently chip away at your hours. Instruction worked for me and I built the time fast.

Yes. Does almost nothing for your marketability but if you bust the checkride it will set you back. Save it until you get off probation at a major (unless your uncle runs the school and your cousin is the DPE).

Fastest path to 1500 first. Then, all else being equal...

Turbine
ME/MEI
135
CFI

In the distant past I'd have said ME first but the current philosophy seems to be show up with 25 hours, and get the other 25 in the sim.

disagree with 135 over CFI. Almost every Regional hiring department prefers hiring hiring CFIs as the payoff comes when they move to the left seat.

CFI is the best route 250 to 750. 135 is a better route 750 to 1500

So where in the pecking order does that leave someone that has 1600 TT, ATP in hand, and 700+ ME (BS, MS, and MBA degrees too)? Never been an instructor as I've been on active duty as a Logistics Officer for 27+ years. All my time is part 91, single pilot IFR with over 1,300 hours cross-country - most being 200+ NM trips all over the US. Would I be better off going corporate? The silence from the regionals I've applied to so far is slowly killing me...

You're quals are truly above and beyond. It's probably intimidating the hiring team 😁😁😁.... just kidding bud.
things are slowly opening up, just give it a few weeks and depending how many places you sent your app almost all of them will be buzzing your phone soon giving you offers

outside hires are going to take a little longer but I see them being sucked up soon. Regionals have to get through their furloughs, CJOs, and cadets first. Then will start filling classes with outsiders.