Wedding gift- new FOiS or aqua terre

Your fiance is very lucky. The general advice is just to take your fiance out shopping. These are great options but it's hard to account for personal taste.

If it was me, though, I'd go for the FOIS.

DSloan has it right. You really can't account for your fiance's personal taste, so it's best to take him shopping and let him select the watch. Although the "surprise" element will be lost, you'll have the assurance of knowing that you are getting him exactly what he wants. Obviously, he's a discriminating man with impeccable taste - he certainly chose a wonderful person to be his partner in life.

I support this message 100%

Also just wanted to throw out a big “good on ya!” to the OP for wanting to surprise their fiancé and also seeking the advice. Looking forward to reading how it unfolds!

I’m going with the minority and will suggest the AT. I currently own a 1969 Speedmaster Professional and have owned many other Speedmasters going back as far as 1976. I also own a 2012 Aqua Terra Skyfall 38.5mm with the vertical teak styled blue dial, which is probably the most sought after AT that is no longer in production:
Because I have owned both Speedmasters and an AT, I think that I have a reasonable basis to compare the two. In my opinion, the AT is the more versatile of the two and really is a stunningly beautiful watch. There is nothing generic about its appearance. The AT also has better specs and features than the FOIS: it has automatic winding (the FOIS is manually wound); a longer power reserve (60 hours vs 50 hours for the FOIS); a date window (none on the FOIS); a time zone function (you can change the position of the hour hand without stopping the minute and second hands, which is great for traveling when you change time zones or making the change from daylight savings time to standard time, or vice versa (the FOIS doesn’t have this feature); anti-reflective coating on both sides of the crystal which makes it much easier to see the dial without reflections (the FOIS has the anti-reflective treatment on the inside of the crystal only); and the AT also has a display case back so your fiancé can view that beautiful movement (no such thing on the FOIS). The chronograph function on the FOIS is nice, but the novelty wears off quickly and then your fiancé will seldom use it. Both are beautiful watches and no one can account for anyone else's taste, but the AT is the better watch in every way.

Green is popular now, green dials everywhere, but Nehru jackets and leisure suits were popular once, too. A don't think green dials will be perpetually attractive.

Probably not, but another advantage that the AT has over the FOIS: lots of options for dial color.