A/U vs. All New

And the big, great worldbuilding extravangza began... and prompty collapsed!

I'm blocked. You see, before nano I was having difficulty with my worldbuilding. I've been hesitating between one or two worlds: setting it in an A/U Elizabethan world and setting it in a made-up world. Both have their own pros and cons.

A/U Elizabethan world:
Pros --> The whole thing began thinking about what would have happened if Christopher Marlowe apart from being a spy was also a magician.
--> Using an A/U gives the story a background that's already there.
--> London hanging in the skies!
--> John Dee as Queen's Magician vs. Francis Walsingham as a Ghost
--> Elizabethan London was very, very cool place
--> The joy of playing around with expectations

Cons --> The straitjacket of reality!
--> The decision of how much to change
--> The fact that not enough real historical characters appear
--> Though I shouldn't be thinking about it, the little voice in the back of my head that says an A/U world won't sell to publishers as well.

All New World:
Pros --> Blank canvas
--> The possibility of creating some really amazing places like GRRM does in A Song of Ice and Fire
--> Just the pure joy of creating a world from scratch which is one of my favourite things about writing fantasy anyway.
--> Strange races, amazing places and some pretty cool organisations I've made up

Cons --> It's not an A/U!
--> What if the amazing places, stranges races and pretty cool organisation aren't that amazing, strange or cool?
--> The lack of resonance with taking away the historical setting.

So... i'm stuck. I have no idea what to do. I've asked my writing friend(s) and posted a new topic on nanowrimo.org to see if I can get some help! Apart from that, I'm relatively lost.

Help! Someone!!!

Joel