My opinion would be to test at 23andMe, then for nominal fee, transfer the results to FTDNA. I have tested here and the other two places I mentioned. I like FTDNA for many reasons the best, but it has the least matches. That said, I have found verifiable cousins (with docs to prove relationship) only here and FamilyTreeDNA (FTDNA).
Here are my autosomal results, with average of new matches per day or hour:
FTDNA (380 days; 1 new match every 14.07 days )
18 Dec 2011 - 18 matches
1 Jan 2013 - 45 matches
23andMe (312 days; 1 new every 2.29 days)
24 Feb 2012 - 304 matches
1 Jan 2013 - 440 matches
Ancestry (156 days; 1 new every 6.82 hours)
29 Jul 2012 - 275 matches
1 Jan 2013 - 824 matches
I am not sure if these were all the starting figures on the first day I had my results, but this gives an indication of how often results come in.