if this is your tile w that counter I'd go matte and use narrower grout line dimension and match the grout to the tile better. I think I'd make another choice however.

I am in the process of choosing backsplash tile. For me I have decided that I definitely want glossy so I will have some reflection to lighten up the space.

Yes- and I am finding that many of the tiles I like only come in gloss or glaze. I think how much window light shines on the tiles is a factor too.

I chose a light grout to transition to the white cupboards, rather than match the quartz counter

I chose matte for two reasons: (1) I don't like shiny/glossy tile, and (2) my decor has rustic elements, with which shiny tile doesn't belong. Point: Depends on the look you're going for and what you like.

I would choose glossy.