In my opinion you are dealing with the New vs the Old. Saint Gaudens has more numismatic value than a current AGE's but in my opinion the AGE's obverse were what Saint Gaudens envisioned his double eagle to look like only with a higher relief (the ultra high relief coin the mint released this year). Even on a MS66 Saint Gaudens you can not get the detail you can out of the current AGE's but it is because
Charles Barber cut it down to a low relief after SG died. Anyway I am getting off the topic..

I would go with a common Saint Gauden's double eagle before a current American Gold Eagle just because you will have more numismatic value (even if it is a common date) and it will keep its value better than an AGE. If you go with a SG just buy it certified (PCGS or NGC) or a good high AU from a trusted dealer. You might want to even take a look at the liberty heads too. (I just like those more..

so don't listen to me if you have your heart set on a SGDE)