I would rather be Seggy than Jtrain. Just in general.
As for Spirit vs. a regional? Spirit. Every day Spirit. Even with weird frog-planes that computers won't let you actually fly - Spirit.
My question is this: There is JC, APC and some others. Not many though. Upcoming interviews, etc have to be pretty easy to figure out. What is the overall value of making a post that says anything other than "OMG! I can't believe I got my DREAM interview! SQUEEEE!!!1"? Seriously - my advice to anyone would be - keep this kind of thing off the internet, keep it among friends you actually know and do NOT express anything publicly other than excitement at the opportunity. That's just my opinion, but I'm probably right - if I saw this just the indecision would make me go for someone else probably.