Which are you more familiar with? Which do you think you will get better marks on? If you haven't already put a lot of effort into revising for the 819 exam, you don't yet know enough to pass it, so go for 829.
If you haven't started your preparation; better option is Java SE 17 ( 1Z0-829) certification. The new certification covers sealed classes, string text blocks, pattern matching in if and switch cases and much more.