Need help with tube selections


Just recently purchased a pair of McIntosh MC-75's. These are my first venture into tube products. I know you can use either KT-88's or 6550's. But which one of these are the best? And, which brand should I buy? Any help would be appreciated. Thanks
jofover
I have a rogue 88 and the best tube I have tried is the electro-harmonix 6550EH. I have tried kt88 kt90 & svetlana 6550b & 6550a. The electro-harmonix 6550EH is nothing short of stunning...thay can be purchased at the tubestore.com
I dunno.... I tried Svetlana KT-88's and the Svet 6550's in my CJ Premier 11a. Still undecided. The 6550's still sound very good to me and I do not hear the HUGE benefit of KT-88's that others describe.