Tube vs. Solid State Amplifiers

I've had both solid-state and tube amps from quite a few manufacturers. In my experience a good tube amp has been my preference however I've heard some pretty ridiculous statements made about tubes. Output transformers and quality of parts play a huge role in the quality of the sound and your experience with the components. Find the sound that you like or want to achieve and then find a way to get there through either one of these solid-state or tube amplifiers or preamplifiers. 

Watts are watts, tube amp just deliver more!
Amps are rated against fix loads (8, 4, 2) but speakers aren't!
Speaker impedance varies a lot, for a single driver it can be 8 Ohm at 200hz but raise to 48 or more at 40 Hz and at 16 or 32 at 15KHz. Multi way speakers tend to be conceived to maintain a leveled impedance but it is never completely flat.
Since Power equals Voltage Square over Impedance, P=V2/R.In a SS amp the voltage rail is fixed and if the impedance rises the power dissipated in the speaker is reduced.In a tube amp, the tube acts as a voltage regulator. Under rising load, the tube will reduce its internal resistance to allow more voltage to be drop on the load thus maintaining or increasing the power output.

@felixa - interesting explanation

In a SS amp the voltage rail is fixed and if the impedance rises the power dissipated in the speaker is reduced.In a tube amp, the tube acts as a voltage regulator. Under rising load, the tube will reduce its internal resistance to allow more voltage to be drop on the load thus maintaining or increasing the power output.

Until I started using a Nagra PSA solid state amp from Switzerland, I thought my tube amps were the best. Similar to what people are saying about the AGD, the transparency is even better and the Nagra has what my tube amps never did. In my experience, at least. 

A SS amps could have a resistor in series with the load. Feedback from the voltage across the resistor provides an indication of the impedance change of the load and could achieve a more tube like sound.