Which bike should I get

I'm a 15 year old guy from Serbia and I should get my A1 license in less than a year,but I'm not sure which bike I should get. Since I live in Serbia a new bike is pretty much not an option, but I was thinking about getting aprilia sx125, sherco sm rs 125(but I can't find a single used one), beta rr50, sherco sm r50 or rieju mrt50. Which one do you think is a best option and why?