There is something of a renaissance going on with resonator guitars nowadays. That's pretty cool because I'm one of those crackpots who uses an old Dobro 33-H for everything.
Johnson is putting out a decent line of guitars for the price, but the fit and finish isn't always spot on. If you are shopping for one check it over pretty carefully for things like the occasional sharp edge of fretwire sticking out of the neck and think seriously about picking up a better quality cone and bridge. The new national cones I've tried just don't have that "it" factor - probably because the embossed swirls they are so proud of are changing the way the cone responds to the vibration of the strings.
Dean and Regal are kind of in the same boat. Both companies offer a solid platform, but will need a bit of tweaking out of the box. That's a pretty minor issues when you start comparing these instruments to what Gibson and National are offering in terms of bang for the buck.
For the price and the cool-factor it's pretty hard to go wrong with any of the "budget" resophonic guitars available today. Just keep in mind that cones and setup are real issues in terms of how these instruments will respond. A guitar that sounds dead in the shop can really come to life with a low action, light gauge strings and a new cone.
Yeah, I said a low action and light gauge strings. The slide routine is a lot of fun, but if you want to play "straight" guitar on a resophonic things get a lot easier if you look at setup along the lines of an electric guitar. The cone is really nothing more than a mechanical pickup so you don't need a GI Joe Kung Fu Grip guitar setup to make them sound good. Make them easy to play, give them room to respond to your touch and all sorts of good things happen.