Different things for different purposes. Mostly, I know what I want to hear so I work tones either from scratch or if there is a preset that's close, modifying an existing tone. But there are times where it's killer to pull a sound match to a recording (Owner of a Lonely Heart solo, Queen stuff, etc). You really see the audience, and band, reaction to that. The tone match function is awesome in this regard. Some of the work I've seen here is nothing short of amazing.
As far as saying I want to play using "David Gilmour/EVH/SRV/Fill in the blank"s tone doesn't work for me, because I don't really play like that. I mean I don't (and often can't) play like them. I tend to think those guys came up the same way. Emulating some licks, but developing their own sound as they went.
I absolutely LOVE the Axe Fx, so no one should take this as a negative statement when I say that the wide wide wide palette of tones it provides might make developing your personal sound a much longer journey if you didn't start on something more... well,
singular in tone. I played Boogies for decades, and it has a heavy presence in "my" tone. Like Townshend and Hiwatt, EVH and Marshall, etc. If I started on the Axe Fx... wow. Young players starting with this will certainly blaze new trails. Time will tell if those trails move anywhere you want to go. But that's a whole other thread.
End vote... Tone from scratch (noting that even "from scratch" has base ingredients)