I used the midstream cassette opks from early-pregnancy-tests.com. I never had any problems with them. To me, it's easier to read than the cheapie dipstick kind and no extra cup needed to dip it in. They ship really quickly too.
Just wanted to add, that we also ordered the FertileAid for women & men and Fertile CM. The two months we took, we got our bfp. 3 big pills of each a day (DH only took 2 a day since he's not a vitamin person.). I took 1 in the am and 2 at night with meals. We did this every day until I ovulated and then stopped. I "think" the vitamins, preseed, opks and charting all worked together for us. HTH!
Last cycle I used the CBE OPKs and got my first positive ever on them. So I recommend them but they were pretty expensive. Prior to that, I was using the cheapie early-pregnancy OKPs that were less than $1 each. It never gave me a positive but when it was 75% as dark as the control line, it usually indicated I would O within 24 hours so I used that as my faux positive.
After 2 m/cs, dx October 2008 with hetero factor v leiden & mthfr & low progesterone; third time was the charm - BFP 3/19/09 on first cycle of clomid.
I used line tests for a couple months and got frustrated trying to decide if they were positive. So now I strictly use CBE digitals and I would never go back You get a smiley face or not, no guessing. THey're not that much more expensive and the difference is worth it.
4/08 BFP resulted in m/c 8/08 BFP resulted in m/c 3/09 Polyp removed and dx MTHFR (both copies) 6 Clomid cycles, all BFN 5/09 IUI#1 with Clomid=BFN 6/09 IUI#2 with Clomid=BFN 8/09 IUI#3 with Clomid=BFN IVF#1 = BFN IVF#2 = BFN IVF#3 ET 2 Grade A blasts 11/16/11 Beta #1: 485 Beta #2: 2,495
Re: ?, ordering OPK's
8/08 BFP resulted in m/c
3/09 Polyp removed and dx MTHFR (both copies)
6 Clomid cycles, all BFN
5/09 IUI#1 with Clomid=BFN
6/09 IUI#2 with Clomid=BFN
8/09 IUI#3 with Clomid=BFN
IVF#1 = BFN
IVF#2 = BFN
IVF#3 ET 2 Grade A blasts 11/16/11
Beta #1: 485
Beta #2: 2,495