I have two of the older style SON, a SP PD-8 and a Shimano LX, so no brand loyalty! The SP is in a 24" wheel, the Shimano is 700c disc and the SON's are 700c rim brake.
For electrical performance, there's plenty of testing and some disagreement about whether the methods reflects real world usage. There's also some differential depending on your speed and the load on the dynamo, not all lights draw in the same way, that's before you get into charging devices. My experience with lights is that they all work fine and the differences are too minor to make it a big consideration. There are some faster audaxers, who say the differences are more noticeable at faster speed, I'll take their word for it, it's not likely to trouble me!.
The older SON is from 2001 and other came in my Raven in 2004. Between them they've been in six bikes and one changed wheel size. They've both been back to Germany for a service, via SJS. One was feeling rough after about 80,000 miles the other was accident damaged, in both cases the cost was £65 plus one-way postage to SJS. These older type are serviced without removing the shell from the wheel, the modern ones requires dismantling and rebuilding. Mine are polished silver rather than anodised and polish up like new.
The SP is four years old and in my folder, I wasn't going to bother but they were on offer and I needed a new front wheel, so... I've had no problem with it, though it's my least used bike. The light flickers for a bit longer when setting off than it did on another, this is despite it being in a smaller wheel. We're not talking about a lot, by the time you get to about 7mph there's no difference. The flanges on the SP (And the rebranded SP's like the Jtek on offer at SJS) are narrower than the others, that wasn't a concern on my folder, but it does build a weaker wheel and if I was planning on tourer use I'd choose something else. They are not user serviceable and there are reports of bearing failures, ususally due to poor seals, though I understand they have been improved. Out of warranty the UK distributor has been offering replacement recon units for £25, though there's nothing I've seen that guarantees they'll always do this.
The Shimano is the youngest, just a couple of years old, it's what you'd expect from Shimano, it just works. Again not designed to be user serviceable, though there's youtube vids of those who've successfully opened and repaired.
Phew, didn't mean to write so much... and I haven't answered if it's worth it, I don't know, but if I wanted something to last a lifetime I'd buy a SON
If you go for a SON and you're using rim brakes and you want the strongest wheel, there's a wide bodied version. Originally made as a special for Peter White in the US, they're now generally available. And thinking of Peter White, it's probably has the most informative dynamo info out there.
https://www.peterwhitecycles.com/schmidt.php