I'm voting Plaid Cymru. Plaid tend to be a bit of a mixed bag in terms of political alignment due to being primarily a republican/nationalist party, but they've been outflanking labour from the left (even in the senedd where labour tends at its furthest left) and holding them to account a lot better than other opposition parties.
I'm expecting labour to win and continue the tories' policies, so smaller more soccdem parties like Plaid gaining seats might help reduce the harm they cause (especially in regards to trans rights, where labour has gone full Rowling).
Also helps that their candidate is a local lad while everyone else except the labour incumbent (who's a massive dickhead) have been parachuted in from elsewhere.