Great question, LegoLordPro. Personally, I couldn't choose just one decade of Lego's history to exclusively buy sets from. Some of my favorite themes came from the mid 90's, like Western, Classic Pirates, and The Adventurers (especially popular for its main character - Johnny Thunder, who was even in the Lego Movie!).
However, I'm also pretty fond of the themes released just around the time I first started buying/getting Lego sets, like Alpha Team, Harry Potter, early Star Wars, and especially Studios.
If I could split between two decades, I'd choose 1994-2004. I wasn't a big fan of the color pallet change, however, have come to appreciate the larger library of colors that have come from it. A lot of the more recent 2015/2016 sets look great, though. So, it would be a really tough choice to limit myself to just a 10 year period of Lego's illustrious history.