ARC tubes v. other tubes

I am new to tube amps and have had an ARC VT-100 Mk.3 for about 3 mos. now. I LOVE it! and have never heard my Genesis 500's sound better. Reading threads and posts here makes me wonder what is the deal w/the stock tubes ARC gives you in their amps and preamps? I also have the LS-15 and PH-3 and bought tubes for retubing in Jan. from ARC. I wonder if I should have looked around for other kinds of tubes? Should I definitely do so when it's time to retube my VT100? I have heard of The Tube but wouldn't know how to begin to pick other tubes for my equipment. I have in the past just trusted ARC but now I wonder if I could do better.
Thanks for any info and suggestions.
With the ARC VT100 MK3, you will have to buy 6550 tubes in matched pairs. You should buy them from the Tube Store or Kevin Deal for 50% of what ARC charges. Some people I know have tried other tubes such as the KT88s but end up back with the 6550s. ARC is a rip off for tubes.
from what i understand, big companies like arc pick a tube which is available in large quantities not nessesarily for sound quality to remain uniform in what they supply as stock to everyone. ive bought from the tubestore and i feel you cant beat the pricing and the shipping. they offer overnight shipping for something like $15.
Thanks so much for your responses. Any recommendations for other brands of 6550s? or for the 6922s that come in the ARC preamps?
I have ARC VT130 (which use basically the same tubes as all the VT100's) and I have tried both the KT88's and the KT90's and always go back the 6550c's. Tighter bass then with either. The manufacture is Svetlana. Only buy the 6550's that have the "C" after the number. There are several 6550 tubes, again only with the "C" after the number. As stated in one of the above threads buying from ARC can get expensive, either buy from The Tube Store or I have been buying from a company in Chicago called Triode Electronics, they are an internet company, very good company, they took back some tubes I had had for over 6 months just because the tubes would not bias up in my amp, recommend them highly, good luck.