I've no personal experience, but I've spent a lot of time researching Dr Suporn. I've not spent much time researching Dr Brassard recently, so I can't say very much about him.
I won't post any links since I'm not sure about the sites terms of service, but there's plenty to find about Dr Suporn using google. There's a number of really long and detailed blog posts, some relatively recent photo's of results, and endless discussions by people visiting him and post-ops. The photo's were pretty impressive, but I couldn't find much to compare for Dr Brassard so I've no idea about the difference.
I believe the story about the remaining testis is related to a pre-existing medial condition, and not something that would apply to anyone else. Also I don't think its possible that any surgeon could somehow miss them in any normal normal case.
Dr Suporn's surgery takes much longer than Dr Brassards, and I believe this is a result of the complexity of what he does. Whether its worth the extra effort I don't know, but you'd hope so since it also results in a much more difficult and longer recovery - double by all accounts.
Dr Suporn requires patients to stay for about 30 days, during which time he does revisions as necessary, and the level of care is apparently excellent. Dr Brassard's stay is I believe about 10 days. Even accounting for the more invasive surgery I find that very reassuring with Dr Suporn, since there's a chance to get everything sorted out before flying home. The last thing I'd want is to fly home and have problems. If money is not an issue then flying business class would no doubt make getting home a lot easier. The extra recovery time with Suporn might be a problem if you have to get back to work soon, especially if you do heavy physical work.
I've seen one or two pictures of Suporn results that looked kind of odd, and possibly related to the excess erectile tissue issue. I think it's a result of swelling that takes a really long time to go down, but once it does it looks normal. I'd guess the swelling is related to the complexity of what he does.
I'm not really sure what to make of a lot of what I read, since almost every seems to be happy with their results no matter who they see. There also seems to be stories of unfortunate results from all surgeons, although some a lot more that others. Suporn definitely has one on this site.
They are both obviously among the very top SRS surgeons in the world. I often find that when a choice is difficult its because there's not much difference, and then it doesn't matter much which choice you make.