I am not familiar with a summon undead so I will assume you mean Create Undead.
Create Undead allow you to get a much more powerful undead minions being a ghoul though you only get three of them. You are able to have them around for 24 hours before losing or recasting the spell again to keep. Further it requires a bonus action to command one or all. If you use higher spell slots you get more powerful undead options (ghasts, wights or mummies).
Danse Macabre gets you 5 zombie, skeletons or a combination of the two. The duration is only for an hour however all of the creatures get attack bonus equal to spellcasting modifier. If upcasting you get two additional ones of your chose.
The prime difference is quality vs. quantity. Create Undead gets you a better type of undead monster but you are limited to how many there are. Danse Macabre provides multiple undead creatures but they are of a weaker variety though do get a nice little bonus.
From the top of my head that is the pros and cons. But really if your going necro and at level 10 just take Danse Macabre now and in one more level you will get Create Undead. Both have their merits of when one is better than the other.