Fridge21

I have a 2013 STX and I tow a Wolfpack toy hauler. Soon I'll be adding a leveling kit and 34" tires to my ride. With that in mind I'm trying to decide for the rear of my truck on whether or not to use a Helwig pro series helper springs http://www.suspensionconnection.com/61902-f150.html or an airbag system either helwig or firestone...thoughts?

TXB421A

I just purchased the Hellwig and have used them in the past.
IMO Air bags are better if you have a stock height truck and only occasionally tow/load the truck up.
For me I put ~400# in the bed every Winter to give me some additional traction in the snow/ice and that weakens the rear leaf springs. And the bonus is that the 400# is traction sand, just in case I am near someone who needs a little help.
The Hellwig offer just enough support to keep the truck level and help the OEM leaf springs not sag as much.

Driftboater

Another option to consider is an AAL. I have a topper and Bilstein 5100s at all 4 corners- the fronts are set on 1.5". I was almost perfectly level but the rear would squat when I added weight or tow the driftboat and would start to ride nose high. I installed an AAL from http://www.generalspringkc.com/Add_a...012_s/1995.htm - the 998lb rated set- and it keeps my rear end from squatting without affecting the ride. A few others on the forum have installed them as well with good results.