Both the Bottlehead and Billie are excellent. I have done the Billie. It is an easy kit to build stock. It has loads of modifications that are well documented online. It could probably keep you busy for a year or just leave it stock and it sounds very good. I've heard it pushing about half dozen different speakers and it always does quite well if the speakers are right for it. A nice thing about each of these amps, if you are doing your first DIY, is that there is loads of online info and a forum for each.
You can order the Billie with a power transformer that has a 2.5V filament supply and 320V HT for B+ so you can build a 2A3 or 45 based amp too.
I also suggest the grid choke mod.
I have some info on online electronic resources for tube DIY. Drop me an email if you would like a copy. If you are starting out it might be helpful.
Happy New Year:
I remain,