ValgallaWolf, I only play HotS with people on fairly large maps. And even then, we don't attack each other until we've defeated all the computer opponents. So, it turns out to be a rather long game, and we almost always get around to training our heroes. I've never played online. There, of course, a different tactic is needed. And I'm most skilled at completing campaigns.

Machines are often offered to players in any game. I just prefer to take other skills. In a long game, skills that enhance the strength of units are more useful than machines, which a good Chaos Knight can destroy with a single Magic Damage attack (IMHO). Machines are good in a short game. I upgraded Ornelle's machines in the first mission until she transformed into a Necromancer.