That's a tough call, and I'm not going to stick my neck out and pick one. They are both good arms. The Linn has some colorations, and the Rega is more neutral. The Linn has a higher quality of construction throughout, and is very articulate. It also has VTA adjustment. I do think that a modded RB300 would beat out an Ittok.
Linn Ittok vs. Rega RB-300
I've been using a Linn Ittok tonearm on my VPI HW-19 Mk II for about ten years. Prior to that I used a Rega RB-300. When I got the Ittok I put the Rega RB-300 in the drawer, thinking it was an inferior arm, and have not used it since. In the past few years, however, I have seen a lot of positive views on the RB-300 and not much on the Ittok. Question is, is the RB-300 really an inferior arm or is it in fact as good or better than the Ittok. This could be especially true given all the mods available for the RB-300. For those inquiring minds I'm currently using a Benz Glider but I haven't tried installing it on the RB-300 mainly because of time.