There is no "Best". How much do you want to spend? How much have you listened to SETS? I have never heard an amp that is best for all applications or all types of music.
For the price of an expensive SET you can easily get two or three great SETS and tweak them into great ones. Most all are compromises of one sort or another and differ with regard to circuit design and therefore sound. The Bottlehead Set mentioned above, for example, uses SS rectification and "parallel feed" which lightens the job of the transformer. Not 'better" or worse", just gives a distinct sound (It is a very nice piece and quite different in its approach.) In my opinion that kit would be a great place to start with SETS if you want excellent sound and you want to learn what SETs are about.
If you do not want to solder every once in a while my advice is to not blow the bank on your first SET. Get a used unit that has good resale in the secondary market(easy to sell when you make the next step). Do a lot of careful listening and see what you like about it with various types of music. Learn a little about about how they work. Again, one nice thing about SETs is that they are comparitively simple. You can tweak them fairly easily to suit your own ears/room/music. This is a great advantage if you ask me. It's like home cooking. You can cook to your taste for 1/15th the cost of a big name restaurant. You can have a 300b and a 2A3 and more.
If you take the "best that $$ can buy approach" you will spend a lot of money. The biggest thing you pay for is the low number of units sold (thus no volume and a high per unit price.) If you have not interest in tweaking I guess this doesn't help.
Finally, I hesitate to say this, but the one guy who posted above (nothing worthwhile in the US/ $$ will buy everything) sounds like a complete fool to me.
Cheers,
