Re: Assume sound quality is equal: Digital or Analog?
Both - of course!! (Like matched vs. traditional grip.)
But either way make sure you're using the best stuff you can afford!
You know what added to the 'analog is better/smoother' hype? The fact that in those days technology simply wasn't any better than it was - not saying it was bad - it was... limited from today's perspective but on the other hand folks at that time manufactured gear to sometimes _higher_ technical specifications (component selection, overall build quality) than nowadays! Those components were more 'forgiving' in terms of signal processing and the signal flow within the equipment was 'slower' than nowadays. This resulted in the overall sound being less harsh (having less or smoother high frequencies) and the transients (fast level bursts which by far exceed the average level) were more prone to being reduced simply by the components, not by design.
Nowadays gear tends to sound cleaner or, if you want, 'harsh'. But that's not because the gear is crappy but because there's more left of the original sound than there was in the past. That's a somewhat simplified version. We _do_ have crappy gear nowadays but you get the idea.
Personally I like using (hi-end) analog gear as front-end (signal -> mics -> analog pre-amps), then (if needed but usually yes) I'd add EQ and/or compression (analog also), then convert the signal. After A/D conversion I'd either use digital stuff or sometimes add another D/A stage for further analog processing. While there are stunning plugins if you once set your hands on really great analog gear and learn what analog stuff can do to the signal (literally within a few seconds you can have noticeable improvements when e.g. using an EQ and turning real knobs instead of fumbling with a mouse at the PC) analog does provide a sound quality to dream of and gives you a great feel of having control over a sound. Plus having real knobs at one's fingertips is just different from clicking in menues.
Provided you have decent gear there's not much of a sonic difference. The difference becomes really obvious when you compare so-so gear (from both worlds).
Converters are a critical component because regardless of the processing quality of the gear itself a crappy D/A converter will make you think that piece of equipment is crap. And modern converters are extremely high standard (money provided).
Just recently I've bought the very best guitar modeling/fx processor around (Fractal Audio Axe-Fx II) and for the first time I really feel I'm not playing a modeling device but a real instrument/amp. In fact I'm considering selling some of my guitar/analog processors/effects because that digital thingy makes so many things extremely easy (endless routing/editing/saving options, all within _one_ unit - plus MIDI footcontroller). I do have a decent Mesa/Boogie tube head sitting at my homestudio but the sound difference is shockingly tiny if inaudible (provided you have a minimum of talent getting settings right/reasonable). I'll keep the amp, at least for now - not really because of any sound difference but because I've paid good money for it, it's decent analog/tube gear and it looks cool! (But weighs a ton...) Haha.
Ultimately I'd rather go with great analog front-end plus mediocre A/D converters than crappy digital.