It is hard to offer any meaningful generalizations about the differences between pushpull and single-ended triode (SET) amps; there are many good and bad examples of both types. I am personally a fan of lower-powered tube amps and I own both SET and pushpull tube amps.
While SET amps are very simple and minimalist in design, this does NOT mean they can be made at lower cost than a roughly comparable pushpull amp because they demand specialized output transformers that tend to be expensive. Because a SET output transformer must be conducting at full power through the primary windings at all time, the transformer must be pretty large even when the output is modest. I have not heard low-priced examples of SET amps that perform satisfactorily. Most of the better sounding triode tubes deliver quite low power when used in SET amps (e.g., 45, 2a3, 300b) so it is quite a challenge to match them with most speakers. There are more powerful triode tubes, such as the 211, that can be used in SET amps, but, the much higher voltages involved make them considerably more expensive if they are to be made to operate safely and reliably.
I think both SET and pushpull amps can be made to sound very good. Recognizing that this is a rough generalization, I tend to find pushpull amps to be more "punchy" (tighter, more powerful bass), but, that more punchy quality makes the sound just a touch more "mechanical" sounding and less natural and relaxed than the sound of SET amps. That is NOT to say that either kind of amp is lacking in dynamics, that is certainly not the case. At more modest listening levels, I find tube amps to be considerably MORE dynamic, lively, and engaging than solid state amps. Of the two favorite amps that I own (both with output in the 6-8 watt range), I slightly prefer my pushpull 349 amp (custom-made rebuild of a Western Electric 133 amp) over my parallel SET Audio Note Kageki (twin 2a3 tubes per channel).
There is another kind of tube amp you should also consider. This is an output transformerless tube amp. These types of amps are capable of delivering astonishingly dynamic and vibrant sound, again, even when overall volume level is modest. Like any other amp type, the specific design and voicing matters, so one does have to make personal choices on the specific model.
While SET amps are very simple and minimalist in design, this does NOT mean they can be made at lower cost than a roughly comparable pushpull amp because they demand specialized output transformers that tend to be expensive. Because a SET output transformer must be conducting at full power through the primary windings at all time, the transformer must be pretty large even when the output is modest. I have not heard low-priced examples of SET amps that perform satisfactorily. Most of the better sounding triode tubes deliver quite low power when used in SET amps (e.g., 45, 2a3, 300b) so it is quite a challenge to match them with most speakers. There are more powerful triode tubes, such as the 211, that can be used in SET amps, but, the much higher voltages involved make them considerably more expensive if they are to be made to operate safely and reliably.
I think both SET and pushpull amps can be made to sound very good. Recognizing that this is a rough generalization, I tend to find pushpull amps to be more "punchy" (tighter, more powerful bass), but, that more punchy quality makes the sound just a touch more "mechanical" sounding and less natural and relaxed than the sound of SET amps. That is NOT to say that either kind of amp is lacking in dynamics, that is certainly not the case. At more modest listening levels, I find tube amps to be considerably MORE dynamic, lively, and engaging than solid state amps. Of the two favorite amps that I own (both with output in the 6-8 watt range), I slightly prefer my pushpull 349 amp (custom-made rebuild of a Western Electric 133 amp) over my parallel SET Audio Note Kageki (twin 2a3 tubes per channel).
There is another kind of tube amp you should also consider. This is an output transformerless tube amp. These types of amps are capable of delivering astonishingly dynamic and vibrant sound, again, even when overall volume level is modest. Like any other amp type, the specific design and voicing matters, so one does have to make personal choices on the specific model.