I've only bought cards to complete a set once and it was XY and even then I haven't completed the set as I haven't pulled an orange Vivillon holo or a Slurpuff Holo. That is my closest set to finishing though.
In terms of ex's I've pulled every card except 2, Venusaur Full Art and Emolga Full Art. The main reason I bought them was because Blastoise and Venusaur's full arts were ones I really wanted and with so many sets coming out I didn't want to buy anymore packs from that set. I bought Emolga Full Art and Skarmory Ex because they were so cheap and figured might as well finish the ex's. I have opened more packs from that set recently though. In hindsight I just pulled a Skarmory ex almost a year and half after buying it and still haven't pulled an Emolga Full Art. (I;ve pulled 3 Yveltal Full Arts and 2 Xerneas Full Arts)
The next closest set would be Furious Fists, I've pulled every card except Full Art Heracross. (I've actually pulled 3 Dragonite Full Arts, 3 Lucario Full Arts and 2 Gold Mega Lucarios...)
I think in terms of a master set, I'm closest with Plasma Freeze, I only need one more reverse, Espeon, 1 ex, Latias FA and 4 secret rares.
From my perspective I don't really see a point in bcbming a complete set, I feel like pulling the cards is more personal and to be honest opening packs is probably the funnest part of collecting cards. There is nothing compared to pulling an Ultra Ball Gold Card from 5 packs or a Genesect Full Art from a tin. It's probably the main reason I own most of the ex's from a set. If I bought I'd probably just buy 1 or 2 ex's from any given set I wanted, I certainly wouldn't own any regular ex's and I probably would have any complete or near complete sets. Like I said just wouldn't be interested.
