Ukulele vs. Mandolin - which should you get?
If you play guitar now and are considering the ukulele or mandolin as your next stringed instrument, one choice is better than the other.
The above instrument is a Fender Ukulele '52. It's called a '52 because the thing is supposed to look sorta/kinda like a '52 Telecaster, but eh... not really. I think Fender calls it a '52 as more of a joke than anything. You could buy one and brag that you own a "real" Fender '52 and you technically wouldn't be lying.
I show the Ukulele '52 for a reason which I'll explain in a moment.
Above: Ibanez M510DVS
Tip on mandolins: If you decide to get a mandolin and it has a bridge that isn't permanently mounted (meaning it comes loose when you take the strings off,) the general rule of thumb is to line it up either at or close to the middle of the f-holes. Why? Intonation. If the bridge is set too far forward or too far back, you'll never get the thing in tune correctly.
If you look at each f-hole, you'll see the middle has a "pointer" of sorts. If you've no idea where to set a bridge when installing new strings on a mandolin, you use those f-hole midpoints as a guide.
Does the bridge need to sit exactly where the f-hole midpoints are? No. It just needs to sit wherever the intonation of the strings sounds best to your ears. Most of the time the correct position will be just slightly behind the f-hole midpoints as shown in the mandolin photo above.
If case you're wondering, yes this also applies to acoustic 6-string guitars with non-permanent mount bridges, violins and pretty much any other stringed instrument that has f-holes on it. When you want to know where to set the bridge, the f-hole midpoints are your guide.
Four things against the mandolin
First, it's usually more expensive than a uke. And that includes the cost it takes to restring one.
Second, it's not all that good as a songwriting instrument.
Third, it's a more difficult instrument to play that requires more finger strength.
Fourth, there's not nearly as much choice with mandolins as there is with ukes.
You can totally buy a mandolin if you want, but don't be surprised if you rarely take it out to actually play the thing. Once the novelty of a mandolin wears off, you may find it difficult if not impossible to use it for songwriting.
One thing (a big thing) in favor of the mandolin
One big advantage the mandolin has over the uke is that it's a far better instrument for live performances. A mandolin is acoustically much louder and from that can be picked up by microphones much easier. You can also do simple street performances with one whereas with a uke that would be difficult just for the fact you really can't hear one.
The entire reason the mandolin is louder is because it's more resonant, uses double the strings of a uke and also uses steel strings.
Which should you get?
If you like the idea of busking (i.e. live street performance), the mandolin is the winner, no question.
If you want something that's better as a songwriting instrument for recording at home, the ukulele is the clear winner.
I especially recommend the ukulele to guitar players who feel they're in a rut and want something that sparks songwriting creativity for cheap. Ukes are fun little things that remind you why you play guitar to begin with.
Can't decide which to get?
Start with the uke first. It's cheaper, easier to play, easier to string up, lighter in weight and arguably more fun to play than the mandolin is.
And again, there are way more ukulele choices compared to mandolins. From the link above you can easily spend hours going through them all.
If you want the choice made real easy for you, get a Kala brand uke. You'll notice nearly every single model gets glowingly positive reviews. There's a reason for that. They're built right.