You can get some decent results with the Subtractor, automating the LFO is a particular fave, adjust the frequency filter to taste. Depends what you're going for really, I find the Subtractor really good for sub basses - set up some square waves and increase the release for an ambient sub. But always, and I mean ALWAYS, chain the device through a Spider Audio Merger & Splitter and wire it across so you can have a stereo output going to your mixer.
The Malstrom is a bit of bitch but once you get your head round it you can acheive some decent sounds, there's arguably more to play with on there than on the subtractor but I find it useful for more mid-range synth sounds. You can also get some wicked pad style effects out of it as well.
You could go balls out and use the Combinator with both of the devices involved but I just simply don't bother because I haven't figured it out!
I would comment on the Thor, but I just simply hate Reason 4's user interface (they've ballsed up the simplicity of the piano roll/creation-production window or whatever you call it) and as a result I've shunned it in favour of Reason 3. But I know how sick the Thor is, so if you're using Reason 4 I'd go for that to create basses.
There's a tutorial on Youtube about how to create a Reece bass in the Combinator but again, it's different course for different horses. I've personally grown tired of the Reece bass.
Hope this gives some form of guidance, sure you'll get your head round it.