(As posted at Guildwars2.com Forum)
The only trap that is worthy of the utility slot is Ambush. The rest should be F3-F4 so we can use them in conjunction with venom.
F1 – Steal
F2 – Needle Trap
F3 – Tripwire
F4 – Shadow Trap
Then we can get new Utility skills to fill the 3 spots.