Heyo! I'm ThatBelgianDude, a Brazilian living in the United States, and I'm a total beginner to speedrunning: I've been following the scene for a while, beyond the AGDQ/SGDQ streams and searching for individual games: it was probably the Tropical Freeze runs that got me interested in the whole thing in general.
To be honest I'll probably just keep watching for a while before jumping into anything because these next few weeks may be a bit crowded for me - but once that's done I'm looking into games like The Witness and the Darksiders franchise, for starters. Still not sure and it would be good to start with games that are a bit small as to not burn out so I think that'd be nice.
Looking forward to hang around and learn about different tips and techniques, as well as keep on touch with the latest runs. Hope everything goes well and I'm glad to be here!
Honestly do whatever games you enjoy playing casually. A lot of running is grinding out a game, and although some games may be straightforward mechanically, if you just get bored of it because the game isn't something you like, you won't run it for very long. The Witness apparently had a 25 minutes run of it (just skimming a headline) so that would be fairly short.
Wouldn't really base your choice on what other people are doing, just find a game that you've done before or you can see yourself putting 100+ hours into, and start to look around for an existing run of it, or begin to route it yourself.
Don't compare yourself to WR at first, or you'll just end up in a cycle of not being pleased with the progress you're making compared to that. Set goals and try to achieve them; compete against yourself and then as you get experience you can become competitive with a record.