Which would be a better overall round to shoot for best groups?
You will have to buy a few boxes of each grade ammo you are looking at and try them out through your gun. Different and even the same make and model guns will shoot differently between different loads.
Generally speaking, the higher grade ammo will help improve performance as compared to lower end ammo wbut which grade works best for your gun is all trial and error.
This past Sunday, I ran a few different types of ammo through a few of my .22s. My Anschütz 54:18 MSR I know works extremely well with old Fed Ultra Match UM1. That ammo being discontinued for a few years now does not get shot often from the stock I have left. Tried Wolf Match Extra (which shoots very well through my CZ 452 American) did not shot very well with groups averaging in the 0.7's @ 50 yds. Also tried RWS R50 for the first time through the gun and it was little better. Best was Lapua Midas M with groups in the 0.3's and 0.4' (5 shots). Still not as good as UM1 but it'll have to do for now.
Switched over to my CMP Kimber 82G. Shot with Wolf ME better than the 54:18 but still not that great. Previously, I had shot Midas M through it and it was getting pretty good groups. Tried out R50 and is was shooting extremely well with it.
The CZ 452 also shot R50 very well comparable to the Wolf ME. Shoots Wolf Match Target well also but it is not as consistant through this gun.
So, it all depends on your gun. There is no way around it, you will have to try out different ammo yourself to see what is best. The target rifle shops like Champion Shooters and Champion's Choice regularly sell ammo by 100 rounds (two boxes) for this purpose, for shooters to try out and see what best shoots through their guns.
I've never had any luck with Eley from the Eley primed Remington and Aquila up to the Match and Ultimate EPS.