They both have pros and cons, but they're indeed quite similar.
TIC-80 is less restricting: more languages (Lua, MoonScript, JavaScript, Fennel, Wren), custom color palette, higher res, and widescreen. The main advantage of PICO-8 is its community, which is the biggest of all "fantasy consoles", which means more help, more examples, and more released games.
I'd personally go with PICO-8, because it's more restricting, and thus allows for a better focus (IMO).