i have used several painters over the years, it depends what i want as to who i use.
Argos (bristol):-
Lime crosswork, perfect quality but the colour choice was lost in translation but was ok, posted to and from, several years on it's still good
fat chance buckshaver, pearl white, gil m stickers, looks good all round, dropped in and collected by me, 2 years on it's still good
muddy fox courier comp, paint and stickers by them, perfect. dropped off and collected by me 2 ish years on it's still good
orange nickel P7, stickers by Gil m, lacquered by argos, dropped off and collected by me, still good 3 years on
felt carbon/aluminium road bike, it was matt black, they put a glitter lacquer on it for me, looked cool, posted to and from, sold years ago
bob jackson (leeds):-
92 clockwork, british racing green and gold stickers, really liked it, chipped easy but it was the "flamboyant" paint which is brittle, posted to and from, sold it
92 aluminium O, white with their stickers, looked awesome, tough as old boots, shame it rode like crap! posted to and from, sold it
92 kona explosif, black with glitter lacquer, still looks awesome 4 years on, stickers applied by me on top of paint, posted to and from.
96 proflex, paint only, looks good, no chips after 3 years except from chain slap under swing arm, posted to and from
TJC design, (bristol) (who graphic shack use)
07 clockwork, dropped off and collected by me, very good finish, only minor issue was i think i should have let it harden a bit before building it as the drop out and disc mount flaked a little when mounting parts, i think it would have been ok if i wasn't in such an excited rush to build it.
fat creations (chichester)
fausto coppi galaxy, picked up and dropped off by none other than Dave Hemmings, pearl white, painted stickers, 10 years on still looks good, one big chip from a spanner drop by me, other than that it's still spot on.
K+N finishing, (portsmouth)
good for basic powder coating, their white is really good, their "gun metal" though is more like matt slate grey
take from that what you will, what i would say is that the only paint jobs i have not been 100% happy with have been when i have not dropped the frame in myself and i wanted a bright colour, if you say "gloss black" the painter knows, if you say "bright green" people have different ideas on what that means. this is why the posted frames have been relatively simple jobs, whites, blacks, silvers etc. also when i post stuff i email full details and pictures before hand to confirm sticker type and placement, i then only put my details in the box with the frame which means someone HAS to look at the emails before painting, doing this i have never had a sticker mistake etc, unless i got it wrong!
regarding posting, my view is it is not ideal, usually i wait until i happen to passing the place i want to do the work to sort of lose the costs a bit. but then i'm never in a rush.
another place i would try is hydrographics , (yorkshire?) various frame builders at the bespoked show last year said they used them.