This sort of thread pops up every once in a while and I think it's funny how my individual response can change from month to month.
I enjoy answering the OPs question and then going back a few months or even weeks later and having a totally different list.
Right now, my core four is:
-Northwoods
-Peterson's DNR
-Plum Pudding
-Blood Red Moon
I thought that was a fun idea, to come back a couple months later and revisit the question. When I first replied to this thread I was really in that, "aggressive discovery" sort of phase where I was constantly trying new blends and had a long list of blends I still wanted to try. Over the past couple months I've pretty well blown through that list of a couple dozen tobaccos I wanted to try and over the course of it my favorite tobaccos list grew from 5 blends to 10!
Cult - Blood Red Moon
Mac Baren - Vanilla Cream Loose Cut
Super Value - Bourbon Whiskey
Cornell & Diehl - Autumn Evening
Gawith Hoggarth & Co. - Kendal Black Cherry
Gawith Hoggarth & Co. - Ennerdale Flake
Gawith Hoggarth & Co. - Bob's Chocolate Flake
Peterson - Early Morning Pipe
John Middleton, Inc. - Carter Hall
Cornell & Diehl - Haunted Bookshop
I don't think I'd want to pick just 4 of them to smoke forever and never smoke anything else, but if I reaaaaaally had to choose 4 then at this point I'd go with...
Gawith Hoggarth & Co. - Kendal Black Cherry
Mac Baren - Vanilla Cream Loose Cut
John Middleton, Inc. - Carter Hall
Cornell & Diehl - Haunted Bookshop
Again though, I sure wouldn't want to have to narrow it down that far since I'm pretty darn pleased with my 10 blend rotation and really love them all.