The reason one would buy steel instead of carbon these days is ride quality. If you've ever ridden a well made steel frame, you'll know what I mean. Steel is,, well,, fun! No other way to put it. The bike just feels alive under you.
Racing, no contest. Well made carbon wins. But riding for ridings sake. Steel wins. Well, with most folks. My idea of a fun ride might not be someone elses.
Yup, fun is subjective. For me, a fun frame has to be stiff (and preferably reasonably light, although I accept that you can build a very light bike with slightly heavier frame). Fun, engaging riding involves stomping up short hills out of the saddle and front end stability for cornering, and there's nothing worse than a flexy frame to throw a damper on that. The steel frames I've ridden have all felt mushy out of the saddle and a bit flexy at the front end, although I've yet to try a really bang-up-to-date one such as something made from oversize XCR. I currently have 3 bikes, two carbon and one Ti, and have previously owned an early 2000s vintage Mercian made out of Reynolds 725. One of the carbon frames is perfect, stiff and handles brilliantly, the other is a bit flexy and doesn't handle so well. The Ti frame (an Enigma as it happens) is not as good as my best carbon frame but I slightly prefer it to my other carbon frame, it's stiff enough under pedalling and certainly a lot stiffer than the old Mercian (which was a complete noodle out of the saddle). The other big advantage it has is that being made of metal and unpainted, I never need to worry about chipping or scratching it and I can scrub off dirt and oil with a scotch pad if necessary…
"Comfort" has never been a big issue for me in a frame, it's something that can be fine-tuned with seat post choice (on a sloping top tube frame at least) and wheel/tyre selection/pressure. That said, some vertical give in the fork is always a good thing, provided it's not at the expense of lateral stiffness. But forks are nearly always carbon these days in any case, even on a steel frame.
Really, I'm completely open minded about material choice. I'd love to try an oversize XCR frame to see if it can match up to the best CF frames, but by default I remain sceptical until experience teaches me otherwise. I agree with Franklin that on paper, the biggest attractions of steel are custom geometry and looks (if steel looks are your thing). I'm not convinced by the lively/comfortable ride-quality thing, I think there is a pretty consistent inverse trade-off between “liveliness” under pedalling and stiffness, irrespective of material, and that this is basically a function of total lateral frame rigidity (which is probably the real factor determining how much the bottom bracket moves laterally, not the stiffness of the BB junction itself…) It's probably easier to build a stiffer frame from CF due to the greater potential for customising tube profiles, but of course that doesn’t mean it can’t be done with the right sort of steel, probably the only limiting factor is how light an equally stiff frame can be.