Hi, I have the Kilo in my rig and yes at some point I will do a bit of tube rolling with it - something i've done with most valve amps i have owned. Although I haven't looked under the hood yet, I'm expecting to find Sovteks, maybe the ElectroHarmonix/ GT choice, the 12AX7WA .. My personal taste in valve is the telefunken style valves like the JJ ECC83S (premium model) that definitely has a different character to the Sovteks. More upper mids and zingy top end.. Although in some ive found that it sounds like they have less wooly bottom end,mthus making them sound clearer vs the Sovteks.
Reading reviews, valve amp purists say the first valve in guitar amps is the 'critical position' and thus i'd stick the best quality valve in there... But what 'flavour' is personal choice. Mr Foxen is quite correct, if a valve is part of a distortion circuit, then you may have to look at the right valve fornthe job, as say a Mullard sounds different to a GT sounds different to a.. Etc etc.
You could buy a selection of valves and try a few out over a few gigs / rehearsals to see what you like best? Maybe let us know how you get on!
Oh, caveat time, be careful when changing valves!