I can think of several distinct ways to do this:
1. More Merit than Activity (this seems logical, but you may miss out on high quality users who barely ever post, while you include users who post a lot and receive Merit for some of their posts)
2. More Merit than Posts (this is a much better quality indicator!)
3. Percentage of Posts that received Merit (now it becomes interesting!)

I'll give some examples of each category (full data and explanation here):
1. LoyceV ( ). Since the introduction of Merit, I've received much more Merit than Activity, but only 0.38 Merit per new post and only 10% of my posts received merit.
2. gmaxwell earned 7.1 Merit per post since the introduction of Merit!
3. theymos received Merit on 32.8% of his posts since Merit was introduced.
Update: after checking an update for gmaxwell, he fits category 3 even better with 59% of his posts merited.

Depending on which criteria you choose, you can get a completely different list of users to follow. I would suggest a combination (kinda like Vod's BPIP Recognition), but categories 2 and 3 require extensive scraping from the forum to get the numbers for each user.