As I mentioned in the chatbox,
LMMS and
Ardour are some choices, both being open-source and free, but for pure MIDI-making, I'm not sure if there's any programs that's not complete cripe.
Qtractor?
I have not touched these three.
Generally, do try to aim for a DAW like LMMS and Ardour, since they give you some room should you want to do anything else.
Generally, MIDI setup is messy and complicated on these, but I haven't had much luck with lesser tools. Especially since pure MIDI editors wouldn't exactly let you sync up an actual song, should you want to make covers.