How to Find the Best Stereo Amplifier
Budget:
Just like everything else, the first step is deciding how much you want to or can spend. It’s a huge let down to shop around and fall in love with a $1,500 amp if your limit is $500.
Car:
Car audio systems can get crazy. External amps provide more power, and paired with a subwoofer, will get that bass thumping fo’ sho. Very simply, look for ohms, RCA preouts and RMS; power is good. Something that can control the front and back volume separately, and has controls for high- and low-pass filters to set your acoustic levels and protect your speakers will do just fine.
Home:
An amp can really boost your home theater experience. Again, working with a subwoofer will give you that thick bass. Check for ohms, watts, and speaker compatibility. You don’t want to overload the speakers. The bonus to home use is the variety of actual home uses there are once you get going — music, movies, gaming, oh yes.
Shop and Listen:
Just about every thing with speakers has some sort of amp integrated inside the system. It’s kind of a requirement in order to hear anything. 
Transistors have an advantage for playing loud but they can’t quite replace all the quality tube sounds. If you go tube, pair it with loudspeakers to boost the power. Also, arranging your speakers will definitely influence your sound experience whether in car or at home.
Listen for strong timing, the range between the soft and loud notes, and stereo imaging capability (Does it sound like you’re right there? Does the sound fill the space?). How does it manage the bass and treb quality? Some amps can pick up on the sound details at the expense of the song or sound as a whole so that high transparency might not be the best. It’s up to you; this is your sonic space so listen up.
Most electronics or specialty stores will have rooms dedicated to their sound systems and that offers you the best opportunity to test them out and ask questions. I’d bet most guys at the counter are audiophiles of some level and have a sweet setup at home.
Here’s a professional power stereo amp from Yamaha:
Yamaha P35005 Amplifier: $696
Find at Smarter.com: Shop for more stereo amplifiers.
