Upgrade or alternative upgrade?

Here's the question. Which upgrades and for which creatures in the Dwarf Castle do you choose? Please provide the upgrade type and justification in advance. Please avoid off-topic discussions. For example: Mountain Guard, because... Harpooner, because... P.S. There is a similar topic, but I think it would be useful to create it in a separate section so that it is clearly visible who chooses what and why.