The Ship Pipeline is full of ships that can cross over between different duties. Some are better at one thing, while another ship (in certain circumstances) would be your IDEAL choice.
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What activity(s) do you "think" you will wind up doing more than anything else? Make that happen, and the rest of your fleet can serve in 'some other' lines that you feel will also cover less-common functions. Chris has stated some missions will require a certain ship to be used or you can't take that mission!
My current Fleet cover's 98% of anything I can think I may want to try: Having already pledged pretty much every ship but the Big "3":
Idris, Hull-E & Javelin!
All Citizens must FUND your FUN! And you'll want to have FUN while doing so!
Mostly making money from Bounties, raw materials or research.
AND/OR Piracy:
As some will feel it is easier to steal their funds from others. EASY MONEY...(maybe). There will be those that get a kick out of setting up illegal drug labs on some Endeavor's. And, I am for this illegal Trade, as when I think of Pirates stealing from other Pirates; It makes me smile!
DECISION - ANSWER 1 QUESTION (with our limited information):
Can the Endeavor do something (that you want to do) that no other ship can fulfill as well?
Of course a second question of major importance's:
"Will you be alive in the morning once your Wife/Husband finds out how much 'more money' you have spend on a Computer Game!" LOL