There are significant limitations to SET's. Glorious midrange, the best, really, but many people miss the deep bass, high frequency extension and dynamic range that other amps do better, or do not wish to be limited to highly sensitive speakers. SET is not the way to go if your primary listening is rock or classical orchestra.
You should search the many posts about these differences in the archives and various audiophile forums, but you need to listen to them to understand the differences and get what sounds best to you. I generally prefer push-pull triode as a kind of compromise between the extremes of ultralinear/pentode and SET, but not always.
On the spectrum from triode to ultralinear to pentode, power increases, so bass gets tighter and the soundstage moves forward, but the sound can become harsher and you lose some ease and air.
You should search the many posts about these differences in the archives and various audiophile forums, but you need to listen to them to understand the differences and get what sounds best to you. I generally prefer push-pull triode as a kind of compromise between the extremes of ultralinear/pentode and SET, but not always.
On the spectrum from triode to ultralinear to pentode, power increases, so bass gets tighter and the soundstage moves forward, but the sound can become harsher and you lose some ease and air.