I was in a similar situation recently. Marriage #1 was a spectacular mess, but this one is more promising. The contrast led to a funny moment at the reception. Despite the fact that I'm typically a solid public speaker and adept at things like toasts, my best man speech for marriage #1 wasn't great. I did the best I could with the material I had, but it's hard to praise a marriage of which you're highly skeptical to a woman you really don't like. My friend has ribbed me for my failing a bit over the years.
So, fast forward to marriage #2, where I like the bride and generally support the marriage. I wrote an excellent speech that spoke highly of the bride, groom, and relationship. I even managed to quote the groom's favorite band, and I constructed the whole thing without even a hint of the prior marriage that continues to cast a long shadow over the groom's life.
So, what does the groom say when I step up in front of the room, glass in hand, to make the toast?
"It better be a good one this time."
I hope you told him not to try that joke with his new bride that night.