Ask a new banjo player what is stopping them buying, and a huge share will say they cannot decide between an open-back and a resonator banjo. They have read that it matters, they treat it as a quality ladder, and they stall. It is not a quality ladder. It is a fork between two musical worlds, and the right answer is decided by the music you want to play, not by which is "better."
What actually differs
A resonator is the bowl-shaped back that projects sound forward, making the banjo louder and brighter — the sound associated with driving bluegrass, where the banjo has to cut through a band. An open-back has no such bowl; it is softer, warmer, and mellower, the sound associated with old-time and clawhammer playing, often solo or in gentler company. Neither is superior. They are tuned for different jobs.
The weight and feel footnote
There is a practical side too: a resonator banjo is heavier, because of that extra bowl, and an open-back is lighter and often more comfortable for long sessions and for clawhammer technique. If you are unsure of style but know you want something light and easygoing to learn on, the open-back is a forgiving, friendly default that you will not regret.
Stop overthinking it
Plenty of players own both eventually, and many open-backs can take a resonator added later anyway. This is not a marriage; it is a starting point. Pick the one that matches the music in your head, accept that you might cross over someday, and start playing. The deliberation is costing you the one thing that actually makes a banjo player: time with the instrument.