I used to live down that way and had work done by both.
+1 for Rainbow. Been ther more than a few times to have o2 bungs welded
-1 for Cottman. Used to live in an apartment nearby and had to use them when my 700R4 went out (no garage FTL). Needless to say the 1st "rebuild" failed in less than a month. Their 2nd attempt lasted a little over a year before it starting exhibiting the 1st signs of slipping (how convienent with a 12mo 12k mile warranty).