I actually own both of these exact same watches. They are fundamentally different watches, both of them great, very difficult to choose between them.
So for me the exercise is, if I had to keep just one of them and was forced to sell the other, which one would go? I'd keep the BB58 and sell the Aqua Terra 38mm. Make no mistake, the Aqua Terra is a phenomenal piece, with better finishing than the BB58 by a country mile. It's far more striking than the BB58, especially with that blue dial, and many would argue that the Omega 8800 Coaxial is the better movement than the in-house Tudor.
But the BB58 is simply a magical piece, there's absolutely nothing on the market like it, with its combination of vintage aesthetics/pedigree, absolutely perfect dimensions (the diameter and thickness are near identical to the classic five-digit Submariner no date), perfect dial symmetry (no date!), modern movement with a great power reserve, etc. But putting all of the boring specs aside, the BB58 is a slow burner -- the more you wear it, the more it starts to get under your skin and you start to appreciate how well it comes together as a complete package.