Here are the 5 toughest matches to pick, at least IMO:
Hollow Knight vs Tales of Berseria
HK has the seeding advantage (bracket votes), likely the pic advantage (Berseria's box art doesn't scream "Vote for me"), and the advantage of being on the Switch.
Berseria has RPGFAQs and the benefit of being part of a well-loved series. The question is, did enough people play it? Do enough people care about Tales of non-Symphonia on this site?
Persona 4 Golden vs Red Dead Redemption (and GTAV if P4G wins)
P4G should get a boost thanks to P5 and Joker in Smash (I think Joker's appearance in Smash helped the entire Persona series, not just P5). RPGFAQs. Series votes.
RDR did okay against SotC back in 2015 and should get a boost thanks to RDR2. P4G is deeply loved on this site, but will it's "enhanced remake" status hurt it? Does the fact that P4 is only playable on Vita and PS2 hurt it? Handheld games tend to have a low ceiling in these contests.
Monster Hunter vs Sekiro
MH has Smash exposure, is part of a series, has a recent expansion
Sekiro finished 3rd in last years GotY polls.
Animal Crossing New Leaf vs Red Dead Redemption 2
AC will get a boost because of the Switch AC. Has Smash exposure, NintendoFAQs.
RDR2 finished 3rd in 2018 GotY polls. Casual appeal. Isn't a handheld game; appeared on multiple consoles
Dark Souls vs The Last of Us
DS comfortably defeated MGSV in 2015. Part of a decade-defining series. Appears on multiple consoles, not just Sony ones.
TLoU is widely praised for its story and often regarded as the best PS3 game ever. Has a sequel coming out this year.