Focus on one, it's better. It is a huge sacrifice, and I perfectly understand this, since I have sooo many original ideas, but that's it. I can work on multiple series at a time, but when I want to do things well, I stick to just one and put the best effort in it.
Besides, if you keep your interest in only one of your projects, you can come up with many interesting ideas for it, such as cool plot points, foreshadowing, etc. By having just one comic, you can also fix plot holes and inconsistencies, that otherwise, with multiple comics, you wouldn't consider.
Then again, it's all up to you to decide, but that's my suggestion 