I'm now using SZ for my smaller sites and it's converting much better than it was on my main site(dupedb), I guess it's better to have just one link pointing to affiliate than two. And I have noticed that many webmasters put as much as 5 different affiliate links.
I would suggest experimenting with 1link for like 1week and see which did best, SZ has done best so far, in fact both SZ and LD are the only ones keeping they shit up to date, all other affiliates I have seen looks exactly the same with #bgcolor changed in css..lol.
6sales this week with 300sent clicks, not bad I guess.
And also, the other affiliate sites might have higher refund rate due to poorly written FAQ's and stuff, I know torrentz.com owner and was talking with him about affiliate he is using, he said it's very tricky, some days 50% of sales get refunded, sometimes none. I have had 2refunds only with SZ so far.