If I'm not multitasking, I prefer skills that are highly interactive with limited elements of repetition, particularly if they involve playing with friends:
1. Dungeoneering
2. Runecrafting before runespan (GOP)
3. Slayer, before jack of trades, th and all the promotions. I liked the tactical aspects of soul wars
If I'm multitasking, I prefer the most afkable skills like woodcutting