Choosing Latency in an FPU
Higher latency generally makes for smaller logic as it allows iterative approaches to calculating your square root. 

In general choose the highest latency your process can cope with, low latency floating point is Expensive in terms of area and speed (High latency floating point is just small 'e' expensive. 

Avoid FP if at all possible, most modern FPGAs have large numbers of fairly wide hardware integer multipliers that can do fixed point just fine, floating point not so much.