It's such a matter of preference. I had some Mullards in my pre (AT and AU) and thought them slow and mushy in the bottom end and rolled off at the top. In my system for my preferene, I settled on 50's vintage RCA Blackplates. Enough euphony in the mids, sweet top end, but still kept the bottom end right.
To each their own.
As the saying goes "Ya pays yer money and takes yer chances"
Bryan