I posted here previously & got no help but thought I'd share what I decided to do. I think I'm in a common boat: business traveler trying to get miles for free economy vacations. Here was my situation:

(1) Home: IAD/DCA
(2) Fare types: cheap economy for travel, business for work
(3) Miles/year? 50k bus, 5-10 pleasure.
(4) Do you have any kind of status at present? None
(5) What is most important to you in a FFP? economy availability for vacations, long-term lounge entry.
(6) Which routes do you fly most often -- IAD-ADD-DAR [Tanzania]
(7) Preferred Airlines -- No preference
(8) Do you travel for work or pleasure? I fly international business class for work, and want to use miles personal trips - 2-3 domestic and 1 international per year.

I fly Ethiopian about 5x per year in business class IAD-DAR, which racks up miles: but United has no bonus for ET flights, so I wanted to see other options. I don't know for how many years I travel, so I wanted to get status that would last for years after work stops paying for it.

What I decided to do:
One roundtrip ticket on ET got me instant Gold Status on Aegean, which gets me lounge access in US & abroad as long as active. All of my other miles on United still, because their award chart is at least hackable with stopovers & open jaws. Hope this helps someone: if others think this is a bad idea, say why for all of us!