I've seen this debate happen a few times, and I'm still not sure which is better...
Pros of Amb/Amb
+ If they don't collide, you start the match with an early "tennis lead", which can snowball pretty quickly, especially if you can pick up a village.
Cons of Amb/Amb
-Early economy is kaput even more than normal. You're rarely getting a $5 card before the 2nd reshuffle
-If they collide, your early economy is REALLY kaput. Doesn't matter how slim your deck is, if their deck is reasonably sized and has 3 more Golds you're probably going to lose.
Pros of Amb/Silver
+ Early economy boost useful if there are some higher cost cards you need fast
Cons of Amb/Silver
-If the other player gets Amb/Amb and they don't collide, you're in a bad spot.
-Your early economy boost might not mean much, since you want a 2nd Ambassador on turn 3/4 anyways.
Does anyone here have more to comment on/say about this? Or how about Amb/non-terminal $4 openings?