My main attempts with speedrunning have been with one of my favorite games, Mega Man 2. The game is short and if you know what to do is quite easy. I don't always remember the boss order for every Mega Man but I do for 2. This was one of the NES games I had as a child and played over and over, because we didn't have much money and so very few games. I like that I can complete it in one sitting as that is very satisfying and somewhat rare with games today. My preferred way to play is on the Switch with the NES joy-con. My best time is 68m14s. I seem to shave off a few more minutes each time, but only replay it twice a year. I have always wanted to play it more regularly, like once a week, but you know...so many games, so little time.
I also like to speedrun through Mario platformers. Usually the first playthrough is a 100% run and my second playthrough is an any% speedrun, but sometimes those collectables get me. I am hoping to try a speedrun of Odyssey sometime this summer.