I've been to many pitch sessions (probably 40-50 in my career) with senior execs at FTSE 1000 companies, and I can assure you I have never competed against Deloitte with any of them. The usual competitors include McK, Bain, BCG, ATK (for Ops strategy type work), BAH, and some boutiques. I guess if Deloitte thinks they compete against the 3Bs, more power to them. I highly doubt that the 3Bs think they compete against Deloitte!!
Now out of the Big 4, I agree that both ACN and Deloitte are probably the best two. Whether one is better than the other, you'll have to ask someone else. I'd consider them equivalent -- but I'm no Big 4 expert.
Most MC firms are sweatshops at the lower levels. I think that McK/3Bs probably work their associates even harder than the Big 4. The question is wheter you're compensated adequately for the work, and whether there's light at the end of the tunnel -- in terms of promotion opportunities or exit strategy. That's a topic for a different thread.