Biasing is not that difficult. Just requires patience and a multi-meter. Many amps are self biasing which is great. Plug in the tubes and go.
There are a lot of different tube types out there. 6550 or KT88 amps are popular because they deliver a lot of power and the tubes are usually inexpensive.
EL34s deliver a more traditional sound profile that you would expect from a tube and it is the classic PRaT but they aren’t as powerful.
845/211s deliver AMAZING soundstages but the tubes can be unreasonably expensive, they run at such a high current you want to be cautious who you buy from as build quality really matters.
300B/520Bs tend to have lush mid ranges that many find massively addictive. Gorgeous sound with lots of detail, many seem these the ultimate tubes. They usually are in SETs (single ended triodes) and are low power, 10w. I can think of a push-pull that delivers 40w and some parsley SETs that deliver 18-28w.
Triode, pentode/tetrode, ultra-Linear, etc are different writing configurations that have to do with the amount of power going through the tube.
In general (some will argue this and there are exceptions) triodes sound the most tubelike. Triode’s deliver the most detail and tend to have the most dimensional soundstage but you get a lot less power out of a triode and often, bass will suffer and be a bit flabbier. Some tubes can only be configured as triodes like the 845.
Pentode/tetrode gives much more power with a more linear frequency response and much tighter bass but usually at the expense of fine detail. This is not always true as you can design a pure pentode that can deliver detail and a fine soundstage like the McIntosh MC275. Amps with a pentode/triode switch
Ultra-linear modes tend to be a little less powerful than a pentode, deliver tight bass and a bit more detail. When you hear someone say that a tube amp sounds solid-state it is almost always in Ultra-Linear.
There are great, detailed explanations of the circuit types out there. I am making generalizations here. I am also trying to keep this simple as I am not sure you care about circuit design.
There are always exceptions and there is a matter of taste. I have a pair mono-blocks that are 6550 based. I love them in triode and found tetrode disappointing. People have challenged me and said I am crazy, they only listen in tetrode.
Personally, I like 845s the best of all tubes. I am addicted to a massive and dynamic soundstage. Others love lush mid-ranges. Others love that classic PRaT style sound and some want a more solid state sound with a more dimensional soundstage.
Full disclosure I am the importer of a very high-end line of amps and we happen to sell triode amps almost exclusively. I have a couple that can be configured as pentodes/ultra-Linear. I rep the line because I love it’s sound profile and prominently sell 845s and 300Bs. My biases are obvious though and hopefully this is still helpful. Good luck!
