Hellwig or Roadmaster sway bar?

Either one. I installed the standard Hellwig bar before the Big Wig was introduced. Even the standard one works fine, and I have a heavy TC. Either one will make a considerable difference in improvement.

have a roadmaster on my truck, works great.

Either are good. Roadmaster uses a better grade of steel so I would go with it if you have the option. For my GM truck only Hellwig had a model that would fit.

With Hellwig in particular be sure to open the box and verify that all the parts were included before you start. They have a reputation for shipping out the bars without all the parts or even with the wrong parts.

the roadmaster is bigger than the hellwig and bolts right in to the F350

I had factory swaybars, but installed Roadmasters several years ago, a huge improvement. I bought 'em because they were much stouter than the Hellwig.

I have the Bigwig and am quite pleased with it. This is our fourth season with it. When the truck is empty it corners like a Corvette.

The Roadmaster looks like a high quality item but the price was just too high for me.
Mike

I installed the Hellwig on my Dodge 3500 after I put on our new 1050S. I'm very happy with it, made a big difference over the stock one! and it was only about $260.00 thru Summit Racing (had about a $450 list price I believe, so there's some markup on this stuff)
Thought the directions kind of sucked & thought that they could have supplied larger bolts to hold the brkts to the frame, ( ended up using the old bolts). Only negatives that I had with the kit.

I just installed a hellwig on my truck but haven't had the camper out yet to check the difference in handling. I did notice on the Roadmaster site that theirs is a little stouter bar but more expensive. The one that came stock on my older 2001 Dodge wasn't as stout as the Hellwig I just put on my 2005 Dodge.