I went with a SG 6 64gb. I think I'd really like the 6+, but there would also be times when its size would just get in the way. Having demo'ed both side by side, I felt the 6 was a great size and a perfect in-between point between the 5 and the 6+.
I also had money considerations - at the time I thought I was going to be re-upping a contract, so I budgeted for $300 for the device (before AppleCare and a case, taxes etc). I ended up going with the NEXT program because it's simply the better deal (over the contract option), but I still wanted to keep the same budget constraints & manageable monthly payment.
I debated between 6+ 16gb or 6 64gb. Went with the latter - after 3 years of 16gb, it's just not enough space. This past weekend I was able to shoot some video of my daughter at a sporting event using the 240fps slo-mo option, edited it, and produced it all on my phone. In the past there's no way that happens - even with no music and limited apps, I'd still only have ~2gb of free space BEFORE considering 8mp pictures and 1080p video of varying framerate. 128gb would be nice, but considering 64gb has been the top choice for so long, it seems like it'll be plenty for the next 2 years of use.
After ordering the SG, I sort of wished I'd gotten the silver/white with a brown leather case. Seems like it'd be sharp. I picked up the black leather case to go with the black phone and it looks really nice, so I'm happy with that - decided it wasn't worth the hassle of doing a return.