I've had both Xperia V and Xperia SP.
In STOCK conditions, I could confidently say that Xperia V > Xperia SP.
Xperia SP may have superior hardware compared to Xperia V but Xperia V has significantly less bugs, a better STILL camera, superb RAM Management, and you even get water resistance up to 1m and 30mins (with that, I would usually clean my Xperia V by soaking it in a dipper filled with water).
However, Xperia V is also ageing well and the same goes with official software updates from Sony. Xperia SP has more chances of getting another software update than Xperia V.
Although Xperia SP has all these annoying bugs, there are plenty of devs who created ROMs that have fixed/mitigated these bugs. The subsequent software update [12.1.A.1.201] has also patched critical bugs such as WiFi issues, Illumination Bar issues, RAM Management (uh, slightly), and others. However some issues still persist such as the screen flickering bug as reported by other xda members (I don't experience this though).
Xperia SP for me has an awesome hardware for a mid-range android device and its performance is only limited by such ugly stock rom. But hey, isn't that the reason why we are here in xda?