As pp's said: all timeless classics , all fairly popular "can't go wrong" choices (and all 3 were on my own list 
- I like names where you can't easily guess age, nationality or social background and with great historical namesakes).
My top pick is William. Can't beat the wide variety of interesting namesakes (The Conqueror, Tell, Scarlet, Wallace, Shakespeare, Wilberforce, Wordsworth, "Billy The Kid", Clinton, Gates... there seems to have been a prominent William in pretty much every field/media), hence it's so well known/used worldwide.
2nd choice Thomas - again great namesakes and international, but it's been the most popular for a while in the UK, as well as having less nn variety than William and Edward if you do get another Thomas/Tom in his school class/social groups.
3rd place to Edward. Really love it, but it is less international - plus I personally dislike the most likely nn "Ed/Eddie" (and "Teddy" is super trendy/popular now too). If I could guarantee the full Edward or maybe Ned, it might be higher for me.