Re: Fender Blues Junior
Tube rectifiers tend to sag, giving a more vintage sound, more touch sensitivity, etc. SS rectifiers don't sag, to the amp is stiffer, better low end, better definition.
It's also possible to get a SS rectifier's reliability, but with "sag". The Weber Copper Cap is a good example - SS replacement for a tube recto.
Another aspect is the economics of building the amp. For a little amp like the Blues Jr., a tube recifier is cheap and easy. For big amps (Twins, 100-Watter MArshall, etc.) the tube recto is expensive and you'd probably need two to power the amp. So, big amps were the first to get SS rectifiers.
For you, what it comes down to is, if you like the sound of the amp, then great. Don't worry about what kind of rectifier it has.