I'd say Firemaking and Cooking, since I got those 2 skills, I did cooking in just 1 week ( Nolifing, not botting ) and Firemaking in about uhh 1-2 weeks, some dude botted it for me
cook wc fletch and fm are horrible capes if you are looking for "coolest" Easiest is thieving and looks nice. Agility doesnt take that long botting it and is very nice. I would rather wear a firecape than fletching wc fm or cooking in fact I did for a while when I had 99 fm and no other 99. Wouldnt be caught dead wearing some trash skillcape if you actually care, and by you making this thread you already showed you care. Take the easiest and most worthwhile. Thieving. 24-7 it and be 99 in 3-4 days. Or spend the money you would waste on some junk skill and buy a firecape service from a trusted member here.