Microspline or HG

If you want a 10 tooth cog it has to be MicroSpline.

HG if you want to save a shed load of £ and hassle/fussiness of 12 speed rear mechs.
You can get close to the same range but not a 10t as mentioned but how often would you be needing a 10t?

FWIW you can get a Sunrace 12s cassette which is HG. I think it's 50 or 51T at one end, but as others have said 11T at the other.

If you can get a microspline 10s cassette to go with your 10s XO bits then that might be the most future proof approach IMO, if you think you may want to go back to 12s at some point.

But on the other hand if you're going to run that bike as 10s "forever" then since I imagine 10s HG cassettes are more readily available than microspline, I'd go HG.

TBH i dont think ive ever visited cog 10, im usually being ebike around about the middle and up on the cassette.
HG it is then.

HG.

I don't get 12 speed at all on ebikes, but as you said you can still get strong 12 speed cassettes for HG.... but also 11 speed and 10 speed.

And while you're at it, get an ebike ready HG freehub. They're just tougher, nothing different about the fit. Hope offer that option for pro5... with pawl alignment that means more pawls engage at once. It'll last longer. Don't bother with the lighter normal pro5 freehub body if buying new.

HOPETECH.COM "https://www.hopetech.com/_repository/1/documents/PRO5_Freehub_11SPD_E_BIKE.pdf"

What @kelvin said. Here's the pile of poo that is Shimano's poor attempt at hub with bearings (not cup and cone) fitted to an eBike:

For an ebike I’ve found the LinkGlide cassettes are vastly more durable than other HG ones.

Deore 10 or 11 speed cassettes are often on offer and having more steel sprockets last longer

There’s one Deore 10 speed cassette which is ALL steel cogs (on an alu body). Just fitted one to my bike. The older one I took off had an alu largest cog.

XO won’t work with Linkglide, will it? The spacing is different on the cassette.

And while you’re at it, get an ebike ready HG freehub.

Would be ideal, but its not happening. Making use of the wiggle/crc deal for a fortus 35 pro5 which is £216. Im never going to get the ebike model for that and the standard one will be more than fine for my pottering.

Ignoring the 4 spare forks which we arent going to talk about, these sales have given me a pair of pro5 fortus 30's in 27.5" for the project build, and a second pair of 29" pro5 fortus 30/35 thats going on the ebike, as well as 2 bikes worth of tech4 V4's.

I really need to stay away from that bloody psa thread.

Well, one easy thing you can do if getting the standard freehub from old stock @dyna-ti ... check the pawls... if they're the ones with the hole in the middle... swap them for the solid ones that come in the ebike friendly freehub (and newer stock of the standard freehub).

I like them both, HG is what i have on my ebike for more cheaper options, but the hub is a DT 350, so i have the HG and microspline freehubs and change them to suit.

I've found 12 speed microspline Shimano to be a faff to set up with smooth shifting. But I got it sorted in the end. Although I'm not hugely happy with how floppy the rear mech is. I'm not sure I'd want it on an ebike.
I'm currently experimenting with a 10 speed linkglide /CUES setup (HG freehub). So far nothing is working well so I've ordered more mechs and cassettes having now read the comparability chart more closely on the shimano website. I have noticed that both the cassettes and mechs on linkglide are much burlier and therefore heavier. Primarily it's a system designed for ebikes so weight isnt so much of an issue

Once again the ugly head of mixed bike standards is reared. I was looking around for ages last year for a new back wheel for my XC bike. Trying to find a second hand non-boost centrelock rotor XD driver rear wheel was a nightmare.

Perhaps at some point in future we will be able to just google "rear wheel"