Re: Synplify vs leonardo?
from FPGA point of view I believe Synplify is much better than LS, even if you master the constraint entry of LS, I believe that this is mainly due to some major defects in the way LS optimize your design, for example it removes all equivalent logic even if you used the don't touch constraint, unless you declared multiple signals and each signal should also have its don't touch attribute, unlike synplify which you can with small tricks do what you want and the tool obeys your constraint.
I believe that this is the reason for synplify merit in speed "you can control it more precisely and easily"
However, if you don't have except LS then you should take care of the LS general errors when you are writing your HDL code.