Engineering is viable at 60 due to rocket boots and bombs, the head is a no go really as you get the 3 gem socket one from Zangarmarsh
Scout's Hood. For PvP there are also viable Stamina trinkets if needed. I would say if you went Gnome, engineering is BiS.
Herbalism is also viable, as
Lifeblood at this level gives 240 haste rating for 20 secs on a 2 min CD (40 haste rating over time - 24% melee haste and more energy regen), which is also great for burst.
Skinning gives
Mastery of Anatomy, a permanent 40 crit rating (2.86% crit).
Do not discount Alchemy if you use Elixirs, they give a nice bonus to them and you also get
Alchemist's Flask which at level 60 is a permanent 16 agi boost. Added together they could be as effective as Skinning/Herbalism due to scalings/buffs increasing them too.
My personal choice would be for Gnome - Engineering and Herbalism. Any other race - Skinning and Herbalism. This based purely on damage/burst.
As always, it depends on situation and whether you prefer min/maxing for PvP/PvE/all round.