I had my Cannondale MTB frame/forks done from red to white back in 2006 from Agros, they did a brilliant job on it but noticed it's not very durable as one time I was adjusting the seatpost and dropped an allen key near the bottom bracket which result a huge chuck of paint come off which it was disappointing.
Last month I bought a 91 Kona Lavadome which need a respray job, took it Argos for a quote which it was too much to spend on an old frame, so I thought I try powder coating and see what it is like, they charged me £30 for sand blast and powder coat, it was an excellent job, not as good as Argos but it's alot more stronger and durable finish, I was happy with it and took another old frame and they made a mess of it with too much paint and bubbles on it, I took it back for them to do it again, I got to pick it up this week and I am hoping it will be ok.
I want to have my Cannondale done soon again (cant get on with the white colour) and want it back to orginal colour of red, I will be using powder coating on that bike but with a different company.
If you want an excellent minty and showroom frame, go for Argos but if you want a strong finish or dont want to spend too much on it then go for powder coating, your finish will depended on the powder coating sprayer, if he is good then you will have a good finish, if he is bad then well you know.....