In no order:
1990-91 Upper Deck and OPC Premier: This may be the best rookie crop of all time. Just look at the list of HOFers that had rookies in these products. Obscene print runs is the only thing keeping the prices down, IMO.
2001-02 Be A Player Memorabilia: One of, if not the, first products to introduce a premium game-used piece in every box. Sure, Titanium and Private Stock the year prior had a jersey or patch in every pack, but how many of them were 4th liners that no one cared about? In BAP, you could pull HOFers and all-time greats.
2003-04; In The Game Used Signature Series / Parkhurst Original 6 / Topps Pristine: Two of these are personal favorites, and one is so amazing even though I had no real connection to it. ITGU SS was, for me, one of the best sets, with an amazing rookie class, and autos/game-used of legends and current stars. Parkhurst O6 has been discussed by others, so no real need to go into it further. Topps Pristine has what is probably one of the most unique pack layouts ever. Packs in packs in packs! Shiny! Uncirculated cards! So many boxes checked with it.
2005-06 The Cup: I don't think anyone is going to argue with this one. Not the first premium set ever, but the first SUPER premium set, laying the groundwork for what is now one of the most heavily sought after products every season.
2012-13 and 2013-14 Panini Prime: One of the most ingenious sets in recent memory. I may be mistaken, but I think they were the first to introduce the tie cards? I know UD Black had them, but not sure the year. However, Prime bests Black in that they had amazing game-used from some of the biggest names in hockey to go with the enormous patch swatches that led people to try and collect the entire emblem for certain players or teams.
2015-16 Upper Deck: This one may be controversial. I never opened any myself. But, I think it's safe to say, that with McDavid, this set started the most recent boom of the hobby, from investors coming in, to collectors getting back into the hobby after years or decades away. Everyone wanted in on the McDavid hype, and this set more than others lead the way IMO.
2017-18 Leaf In The Game Used: Another personal favorite, and possibly an unpopular opinion. I know many don't like the use of jerseys instead of player pictures, or the use of sticker autos, but you simply cannot ignore the absolute monster this set is, with the memorabilia that was included, the HOF names among the checklists, and the quality of the product as a whole. Some may not like the endless parallels, but others, like myself, found it quite useful when trying to make sets but not worried about matching foil colors.
Presidents Choice The Vezina Collection: I think this pretty much speaks for itself. With a certain member here buying what seemed like half of the product produced and trying his best to complete the sets (envious, btw, not shaming), this set may be the pinnacle of all things goalie related.
Presidents Choice Solid Gold: Similar to the Vezina Collection, but with a more wide spread appeal, including current and former legends and stars among the players you could obtain.