1. You can choose any link you want (US or CZ) - both will work OK (and most likely will be able to send data faster than your connection speed).
I learned and acquired a useful habit for downloads over the years. If you're offered a number of "mirror" sites to download from (and this assumes you know more or less where they are), I try to pick one that's overseas, especially if it's the wee hours of the morning "over there".
All other things being equal, a server will usually be busiest during the day and evening at
its local time. So if you try at a quiet time there, the download will usually go faster and smoother.
That can backfire occasionally, of course -- a good server operator will try to schedule routine (as opposed to emergency) server maintenance during those quiet hours, to minimize disruption, so the site might be temporarily down, but give it a try anyway.