I have owned about 5 McMillan's and only one Rimrock (current Borden era). I think the Rimrock is good, but would probably go for the McMillan in preference. I have always had good dealings with McMillan - in fact will order a 6th stock off them in the next few months.
As a general comment, I have had very mixed success in my dealings with many diverse stock makers, but either of the options you list will work very well compared to a lot of other options on the market.
Fergus