I'm a mostly-reformed Collector of Musical Instruments and at one time had a frightful number of things I wasn't playing, so when I started uncluttering the house I decided to re-home the instruments by selling or donating them so that they would get played.
Over the past 5 years I've evicted a bodhran (Irish drum), penny whistle, alto recorder, soprano recorder, 4 guitars (electric, classical, 12-string, and 5-string bass), some drumsticks, and a violin. I kept one keyboard, upgraded another one, and gave two more to a friend, and I saved up and purchased a professional-grade B flat clarinet, keeping my student clarinet for outdoor concerts and as a backup. (I've subsequently added an alto clarinet, a flute and an alto sax to the mix, and adopted a Yamaha acoustic guitar that someone had put out with the trash.)
The motivation for doing this wasn't just that I wanted someone else to have a go at the instruments; I wanted to get good at clarinet, which I've been studying for nearly 12 years now. It was just too frustrating to be mediocre on 8 instruments, when what I wanted was to be highly competent on 1 or 2 of them. I had to resign myself to the fact that there simply wasn't enough time in the day to practice them all, decided that clarinet was the direction I wanted to go, and committed to it.
As I see it, Meowstache, banjo is a closer fit with the fretted instruments you already know and would be easier to get up to speed on. It also seems to be less common than fiddle and would add a unique musical texture if you're jamming in a group.
Fiddle has its merits, but speaking as an adult beginner (took up violin in early 40s and got my Grade 3 Royal Conservatory before deciding that I really didn't like it all that much), it has a steep learning curve and requires a particularly keen ear and fine muscle control of the left hand. It's also not great if you're prone to shoulder problems.
Whichever one you pick, or even if you decide to skip new instruments and take guitar or ukulele to a higher level, consider investing in a few months of private lessons with a good teacher. What may take you a month to figure out may be something that a teacher can explain to you in 5-10 minutes.