IMO, banjos are the cat's meow!
If you're thinking of getting started, great!, but there are a few things to consider.
Imagine saying, "I want to take up the the guitar, what do people recommend?" Are you interested in the guitar because you love Segovia? Leo Kottke? Joe Pass? Doc Watson? Jimi Hendrix? How you answer that question will suggest what kind of guitar you might want to start with.
Same with banjo.
People associate the banjo with bluegrass, and rightly so -- Earl Scruggs was an innovator on par with any musician you'd care to name, and he invented and / or perfected virtually every technique employed by bluegrass banjo players of the past 60+ years.
But bluegrass banjo is not the only style.
I'm most fond of Appalachian style banjo, also called frailing or clawhammer.
There are classical banjo players.
The banjo isn't used in jazz much anymore, but the greatest surge in banjo popularity (prior to Scruggs) was when it was used as a rhythm instrument by just about every jazz combo in existence from the '20s to the early '50s. Their ubiquity is why you still see so many vintage tenor (4-string) banjos on the vintage market. Tens of thousands of the (damn) things were sold.
If you like bluegrass style banjo, you'll likely prefer the sound of a resonator-backed banjo, usually played with fingerpicks. These banjos are admred for their volume, projection, and their responsivness to an aggressive attack. (When people describe high-volume guitars as "banjo killers," these are the banjos they're trying to kill.)
If you like clawhammer style, you'll likley prefer an openback banjo, which have more "thump," or "cluck," and are played with the backs of the fingernails and thumb -- no fingerpicks.
If you're not sure, I recommend going to a decent music store that stocks both styles of banjos and taking a whack at them and seeing which you like the sound of. You could also go on YouTube and search for "bluegrass banjo," "clawhammer banjo," etc., and see if you prefer one style over another.
As with all things there are no rules -- you can do whatever you like with any instrument. Buy or borrow one and just fool around with it.
And while G is considered standard tuning for banjo, there are dozens of tunings, many of them associated with specific songs played in those tunings. (As with the guitar, I just make up my own banjo tunings.)
There are also many different kinds of tone-rings, the part the head is seated on. (And some banjos have no tone-ring.) People discuss tone-rings on banjo chat groups with the same kind of sweaty-browed fervor that people discuss rosewood, versus mahogany, versus maple, on guitar chat groups.
