I would go Ampeg. (Of course I would say that!)
As far as the speakers go, I've always liked the Peavey Black Widow 15s. That way, if you blow one, you can just buy a new basket and bolt it on. It's easy. The only problem is that they need some power to really run.
The thing with bass that is different than guitar is the frequencies it needs to produce (obviously). Lower frequencies take more power to produce. That's why singers pull the mic away from their mouth when they hit the high notes. If they use the same projection, the high notes come out louder. That is why you need more power when you are working with bass frequencies. There is a general rule of thumb with bass in a live environment, and that is to have 3x the power behind the bass as you do on guitar. The other thing is with tube vs. solid state, tube is louder with less wattage. A 100 watt tube amp is louder than a 300 solid state rig. So, if you are running a 100 tube head, your bassist needs 300 watts tube, or 600 watts solid state. If you have two guitarists, you need twice that. That is why the Ampeg SVT 4 Pro is on the market, at 1200 watts (or bridged at 1600 watts).
Also, bass frequencies are produced by surface area. If you do the math, four ten inch speakers have more surface area than a fifteen inch speaker. This is the logic behind the 8x10. The more surface area you have in your speakers, the more bass you will get out of your rig. If he is going for something small, I would recommend a 4x12 bass cabinet. Otherwise, it is really hard to argue with the 8x10 (unless you practice in a basement, in which case there is a very strong argument.)
As far as bass tone goes, there are really two different sounds. One is the fat, meaty tone that is well rounded and deep, and the other is more of a nasally and poppy brighter tone. Both can be bass heavy or punchy, but there is i difference that is kinda similar to that "weird mids vs regular mids" debate in the guitar world. The first tone, the rounded tone, comes from brands like Ampeg or Mesa. The second tone, the nasal tone, comes from SWR or Gallien Krueger. Granted, you can dial them all in to cover a similar ground, especially GK stuff, but it's best to cater to their unique nuances.
I hope that helps with the bass quest.