I only ever used one ship, up until the point I finally got my clipper fully kitted. Now I use that for undermining bounty hunting and have begun to build specialized ships for other purposes. I fitted a Diamond Back Scout for smuggling runs because of its great jump range while still having enough cargo space for most of those missions. It also seems to be harder to scan (if my experience going up against them is anything to go by). I am now working on saving for a type 7 to outfit for mining or trade runs (I may just save for a Python).
I really don’t like refitting my ship for different roles. The Clipper is a good all rounder but I don’t enjoy flying out to a high tech station every time I want to switch from killing thing to trade runs or even mining for that matter. Now that I have enough earning potential I am going to focus on having specialized ships for whatever mission pops up that is most profitable or what I fell like doing at the moment. This is especially important for me since I have limited time and any time spent refitting my ship is time that I’m not making more credits.