I use Hotrox, never had a problem with them.
Good idea to keep a spare of each, but if you look after your amp, you'll probably never need them.
I spoke to Denis Cornell about this shortly after buying my amp, & he reckons it's a bit of a myth about
valves blowing, and that modern valves should last years if looked after.
If you look on Watford Valves website they have tested & reviewed loads of valves, modern & nos.