Alright I have a limited amount of time on the X95, more time for the SL8, but disclaimer I haven't done any extensive testing on both as far as ammo preference, just basic bulk 55gr federal, 62gr m855 federal, and some 69gr swiss p target(very limited number of rounds).
So I'm breaking it down on the two paragraphs
SL8:
Pros: Accurate, this is probably the most accurate out of the box autoloader i own(with appropriate ammo), with swiss p target you can comfortably do 0.5 moa 5 shot groups at 100. with the bulk stuff it's much less impressive around 1.5-2 moa. The gun is also phenomenally clean in the action, due to its design and sure you can go 15k without cleaning but why push it that far? The trigger is quite good for a factory gun. The weight of the gun makes it a fairly soft shooting gun. The gun is truly ambi friendly.
Cons: Weight and balance, this is a nose heavy gun thanks to its nose heavy barrel, and a generally heavy gun. The bore offset is huge with magnified optics, less so with a low mount unmagnified optic. If you don't convert the magwell to ar mags the factory mags are typical Hk, very expensive. The barrel not being threaded is a big fail for me.
Meh: Some people hate it, I don't mind it but the thumbhole stock. It can be a turn off for people.
X95:
Pros: The compact form and the excellent balance, this is not a particularly light gun but a lot of the heavy bits sitting behind your pistol grip makes for one well balanced gun. This gun has a lower bore offset than the SL8. It has a threaded barrel in a common ar threading, and stock has ar based controls, and takes ar mags.
Cons: Trigger is mediocore at best, accuracy is acceptable for a fighting carbine but it's nowhere near a SL8 especially with match ammo this is a 2 moa gun on average 1.5 on its good day with expensive ammo.
Meh: Some people hate the bullpup ergos, some love it, I can't tell you what you like, I am predominantly AR/C7/C8 with my shooting till OIC, so to me it's awkward, but I'm sure with adequate training it could be fine.
TL

R The SL8 should be your choice if you want to usually take this to the range and shoot for accuracy, for action shooting such as 3 gun competition x95would be the handier option of the two.
Edit: Little education time on anyone purchasing any european manufactured firearm, due to legal gubbins they have to mark it 223 Rem instead of 5.56x45 when selling to civilians . But by european standards they measure it by CIP standards rather than the SAAMI standards, and by CIP standards 223 Rem and 5.56X45 is the same thing, so this is not just the Hk but any european manufactured gun that says 223 Rem should be able to safely chamber 5.56
Hope this helps.