Countries (preferably close to you) are probably the most important factors.
You might also want to consider using reflector options
-
--age 2(or larger, use a small number, means hours after last mirror update) --protocol https-
--latest 10(or even 20)
Note that option --sort rate makes ranking usually very slow. By using countries you may not need to use rate option at all. Also using option --sort country may be useful.