First point: the 2 batteries you link to seem to have different measurements. Will they both fit in your bike? 175x87x155 or 185x80x170?
Both are sealed for life, maintenance free. The gel and AGM (absorbed glass mat) are just different ways of holding the electrolyte to improve efficiency. AGM seems to be taking over from gel on most new vehicles.
I have an AGM in my bike and would be happy to fit the cheaper of those two to my bike in the appropriate size. One advantage of the AGM is that they won't leak if the bike has a little lie down because you drop it or worse.
Exide have a multi-national website which includes a Serbian section, in English at
http://www.exide.com/cs/en/product-...transportation/motorcycle-transportation.aspx - in reality the motorcycle products are identical throughout Europe. It appears the gel battery is not listed and that the black AGM battery is current.