I continuously ask myself why I like BW so much and have come to no conclusion... except that it's BW... but there's more than just that!
Okay. Let's go.
BW is legitimately the best 1v1 tier by a long shot. Look at all the choices you have. Firstly, there's no gimmicks. No mega evolution. No Z-moves. No dynamax (lol ty ss for not having dynamax). The fact that there's no gimmicks makes the metagame so much more straightforward. Secondly, this is the only format with no gimmicks before SS, which had so many mons not be used due to dexit. In BW, I can use a Hariyama! Tell me where else you can use a Hariyama against a Terrakion with no gimmicks! Nowhere! Secondly, look at the item choices. Gems are such a cool edition to a gimmick-less format. You see so many strategies that you just don't see in SS. Charge Electric Gem Thundurus? Sign me up! I'm gonna drop a tbolt to win a match without regards for all the stupid gimmicks that can stop me. The meta is a pleasure to play. There's so many mons, so many strategies, no gimmicks. A generation with all the mons up to that point is obviously better than one without. Therefore, it is my true belief that there is no format better than BW in 1v1.
(sorry, I wish I could make this longer but I have to do things... irl sucks sometimes...)