This is not a standard battle scenario of who beats who on the onset of conflict, but more a power test as to who operates on higher levels all around.
1. Which one of these characters has better energy output?
2. The mysticism test.
3. The strength test.
3. The durability test ( who is tougher?)
4. The better tactician (who can orchestrate preparations better?)
1- Darkseid, but his powers are very inconsistants.
2- Probably Thanos
3- Split
4- Sure as hell it's Thanos
5- Both of them roxx, but I'll say Thanos, who sports probably the stupidest feat ever, with what he did in Marvel: The End (out-prepping Doom, and basically, absorb Marvel.)
6- Thanos has some incredible feats, but I'll go with Darkseid
7- Thanos all the way
Depends on which Darkseid you want to use. If you like him/DC, you're probably going to go with Final Crisis or "real" Darkseid or Soul Fire Darkseid or Pre-Crisis Darkseid. If you like Thanos/Marvel, you're probably use the Post Crisis Darkseid avatar.