The main thing is to get speakers you like and that your amps will drive. With tubes it will not make a lot of difference as they have the output transformer to smooth out impedance. With SS it is a little more complicated, a good SS amp will double its power every time the impedance is halved, so it will have twice the power at 4 ohms as 8. Sounds good but remember that "4 ohm" speakers may go to 2 or 3 ohms in parts of the frequency range, the amp may try to increase its power output there and not have a good enough power supply to do so. So although 4 ohms gives more output 8 is a safer load for most SS amps. The only way to know for sure is to look at the impedance curve for your individual speakers and the power output curve for your amp. See, simple isn't it? LOL.
