From my experience modding on Reddit, it's generally a good idea not to engage with spam comments at all. Just downvote and report them. The ideal outcome is they just silently disappear when the mods get them, and if they've been otherwise ignored it's super easy. If there's a comment chain underneath it, it starts to take more thought and ends up getting messier as it involves either removing ok comments from other users or removing the context for those comments.
Same thing for human trolls. Downvoting is good, but once you engage in them the removal gets more tedious, especially since troll threads tend to spiral out of control. Modding is done by volunteers, make it easy for them, especially since responding to these things usually has very little value. Obvious spam and trolling is obvious to everyone and the downvotes signal to other people to not take it seriously.