New player here - what sets to buy?

Hey fellow players, I am new to MTG. I played one or two games as a kid and now a friend and her partner got me into playing. I bought some LOTR precons and a Hobbit play booster display and a collector display. I build some fun decks with the cards I got but wanna go a bit deeper and wanted to try build a Smaug commander deck, as I got this sick completely golden looking Smaug, the Magnificent (nah just kidding :-P). Now to my problem.

There are SO MANY CARDS. And I just can‘t decide, what set to buy next. I know, I know buy singles not boosters, but thats just not the same for me. I just love opening boosters and hope for some cool cards (and god knows I fucking love those shiny little motherfuckers). I also have collecting tendencies.

So what set would you guys recommend for buying, so I can expand my collection, build some new decks - also for my GF, who surprisingly loves to play but hates to lose haha - maybe contribute to this Smaug/Goblins/Treasure commander deck and maybe has some all around useful and good (and good looking) cards in it? What are your favorite sets and why?

I prefer the fantasy setting above sci-fi and would prefer to buy collector displays over set/play displays.

I was thinking about MH3, Master Commander/Legends, Foundations or maybe some of the D&D sets.

Any help or insights of veteran players would be very much appreciated.

Thank you guys and have a nice day!

TL;DR What sets should I buy next as a beginner dabbling in building a (Smaug) commander deck and expanding my collection. What are your fav sets and why?