oh, and then within the tube amp category there's class A, class B (but class B isn't very common at all for guitar amps; i've yet to come across one personally), class AB, etc. basically efficiency categories.
transistor amps
the good: cheap, fairly long-lasting.
the bad: sound awful at high volumes. not responsive to nuances in playing and changes in dynamics (e.g. picking hard and picking soft will result in the same volume out of the amp.)
tube amps
the good: responsive to nuances in playing and changes in dynamics. warm, without clipping at high volumes due to even harmonic frequencies as opposed to the odd-harmonic frequency distortion created by transistor amps, if i'm not mistaken.
the bad: tubes need biasing and changing, and might blow on you during a gig. tube amps are generally fairly expensive. tube amps are heavy.
digital modelling amps
the good: they're exceedingly versatile - they can sound like tons of different amps. they can go direct to mixers so you don't need to get an amp cab or speakers.
the bad: like transistor amps, they generally lack responsiveness to playing nuances and changes in dynamics. they are, however, more expensive than transistor amps (if you buy a digital modelling amp with speakers). they may be cheaper if you just get the modelling unit and go direct to the mixer. they model lots of stuff but like all imitations, aren't as convincing as the real thing. they are sensitive to spikes in voltage and it's strongly recommended that you use a surge protector with your modelling amp so that you don't lose your settings in the event of a spike. tube amps in this regard are much much more forgiving to spikes.
hybrid tube/transistor amps
the good: they're like transistor amps with better gain at lower volume.
the bad: they're like transistor amps with better gain at lower volume and lousy gain at high volume. tube amps sound great at high volumes because the overdrive/distortion comes from having saturated tubes in the power amp section. hybrids use transistors in the power amp section, so while their preamp tubes may give a decent gain at low volumes, at high volumes your amp reacts like a transistor amp and the preamp tubes don't help that much. i personally think hybrid amps are a gimmick. i say if you want tube, get tube. hybrid won't get you there, but it'll make you pay part of the journey.
cheers.