If we're throwing out new stuff to talk about ... how about my auction that's going on right now, and ends tomorrow... There's at least a few retro games there... NES/Saturn and stuff! https://gametz.com/General_Marketplace/spring-clea...
That being said ... I think Xbox is probably the easiest for complete set on that list, because only a handful of those games have high values on them.
GC probably offers a better quality of game (personal preference), and there's more interesting stuff, but I feel like it's going to cost more than 1k
I have a friend that's working on Dreamcast, and it only makes sense for him because he started before some of those games go gross.
PS2 is just a beast in terms of quantity ... tracking all those down is going to be a mess.
VB is the "easiest" in terms of number of games ... and I've always had a theory that Jaguar would be easy as well, but nothing has ever interested me about that system enough to look into it seriously.