Having made my decision, got Civ5 CE, and put 100 hours into it already, having put in ~120 hours previously on BE, it's incredible really.
Civ 5, with all the DLC, is an excellent game. I see now why it is (still) such a popular game.
BE, which is based off the exact same engine, and uses exactly the same interface, just can't touch it, and there are many, many reasons for this. But the three that stand out for me right now are
1) The leaders. Civ5 has a huge cast of differing characters, all with their own personalities that affect how they play each game. BE has a handful of characters, who look different, but lack personality and have no discernable difference in gameplay.
2) The paths to victory. Although there are a similar number of victory types, the paths to victory in Civ 5 are bewilderingly numerous. I'm sure the uber power gamers with their 100 turn deity victories would disagree as they home in on the optimal solution for every path. But for the average gamer, the diversity in religion and social policies opens up so many ways to skin the cat.
3) Wonders. They are so terrible in BE. So terrible, that many of them are worse than normal buildings. Or come so late that they are of no use. Or you don't even realise they are a wonder. Civ 5 has numerous wonders that are "must haves" throughout the game depending on your chosen path. I never did a single fist pump on getting a wonder in BE, but when beat an AI to that key wonder in Civ 5...
The only thing BE has is its soundtrack, but Civ V's is pretty epic too, so it can't even score a point there.
I'm glad you are enjoying Civ V. This is why I recommended you get it instead. It is just so much more solid on so many levels.
As for the reasons why one is better than the other, if I were to break it down, I would state 2 things Civ V has over BE, superior immersion and game play.
Now get off this forum and go play Anno Domini mod for Civ V!