The RIGHT diesels start just as easily as most gassers, even in the coldest weather. I've owned dozens of each, own 3 gassers and 14 diesels now. The 3 gassers are old family tractors that won't ever again be "go to" workers. I don't own, nor do I plan on owning ANY tractors that aren't in good condition. If I get a gas OR diesel that's worn out and sloppy, It EITHER goes away OR gets rebuilt.
As far as collectibles, either will do. But I don't consider myself to be a collector. As far as WORKING tractors, diesels are king....gassers CAN be fire hazards. When I say "working", I DO NOT mean occasional workers....the 15 or 20 hour a year on 15 or 20 acres of hobby farm kind.....I mean HARD working tractors on a working production agriculture kind of farm or business.... YMMV