A square neck resonator has high action and is played flat on the lap with a steel bar, so the strings never touch the frets. It's usually tuned to an open chord, most often open G. Heavier strings help here because they hold up under a bar and give the cone plenty to work with.
A round neck resonator has a guitar-style neck. You can fret it normally, play slide, or both, and it may be tuned to standard or an open tuning. Some round neck players prefer a slightly lighter feel for fretting, but many use the same sets as square neck players.
Our resonator sets are all medium .017–.056. If you play a square neck in open tuning, start with Nickel (DBR1756N). For a round neck played in standard tuning and with a slide, the same set works.