I'd go for DCA, unless your employer will cover taxi/lyft then IAD is good too.

You can shave some time off by Transferring from the Red to Blue line at Farragut (it counts as a transfer even though you're walking across the square). I used to mobile order a breakfast sandwich from the Starbucks, eat it quickly, neck an iced coffee, then walk across the square

That being said where you're going is the most important consideration IMHO. DCA has really good coverage within the US (anywhere there's a congressman, there's a flight ), but very little international and less selection for long haul flights to the west coast. (It's a security thing, they don't want planes with huge fuel full fuel tanks taking off / landing so close to downtown)

DCA has a lot of international and longer haul nonstop flights (such as IAD -> SFO)

Honestly, I preferred DCA mainly because it's a known quantity.

BWI is an option, but dealing with Amtrak or MARC then metro is a long ride. I'd narrow it to IAD or DCA.

Also, I always found DCA just... smoother. Well polished. I didn't have precheck or anything but security was quick, whereas IAD I'd constantly get waylayed in line.

TLDR: IAD if you can cab or want good selection for long haul/international, DCA for national.
DCA also has a lot of flights to the major Canadian cities if that's a factor (Toronto, Ottawa)