Summon is a good choice especially if you don't have a lot of good gear to use. I would recommend you put a point into amplify damage to give your skeles more stomping power. A clay golem can be a good way to add to your horde of minions too. He slows enemies and is a good tank in the earlier difficulties. Also you would be well advised to go through some of the other guides in the necro section of this forum, lot's of good information to be had here.