I agree with many here that "it depends on what you are trying to achieve".
Some are getting sort of heated in this discussion. I would step back and make the scenario of your best friend wants to purchase the "best amp" for his/her system. Wouldn't the first question you ask be, what speakers are you going to use? I need to know this first. I also need to know your level of music appreciation to determine what you mean by "best". If you couldn't tell whether you are listening to a real instrument vs an electronic instrument, or know what dimensionality, space, soundstage, etc. are, then your idea of "best" is not what others would consider best.
I would also want to know you price point. Within a certain price point and taking the other things into consideration can help determine what is "best".
If you have 102 db/watt speakers, then you really don't need 500 wpc amp. where about 10 watts would drive you out of the room. So for that speaker, you would need a low powered, very clean amp.
If you have extremely difficult to drive speakers, well, that is another story altogether. you basically need an arc welder.
If your listening room is stupidly huge and you are sitting very far away, well, you need something that can help the speakers project.
People have their favorite amps, pre-amps, etc. However, their favorite "best" amp won't work for you if you situation is different.
1. What speakers are you driving?
2. How is your appreciation of music?
3. What is your price point?
4. What is your listening room like?
5. What are your other system pieces composed of?
If I know these things about you, then I can narrow the range of amps for you to demo.
enjoy