4 series or new 3 series

I can’t decide between the new 3 series or the
current 4 series (which I read is to be replaced
in 2020).

Does it make sense to get the new 3 series as
the new look will be the modern design for
many years now?

Or is there a reason I am not aware of as to
why I should get the 4 series?

I do much prefer the 4, but if a new version
came out after a few months of owning the
car it would be very annoying. (Also I won’t be
able to afford a new look 4 series for maybe a
year after it’s released).

Thanks