I've had the base level 27 in with a 256 GB SSD for a few weeks now. For reference, I upgraded from a Late 2012 Mac Mini i7 with a 500 GB SDD and a 1 TB spinning drive with 16 gigs of ram. So far, I am very, very happy. The SSD is unbelievably fast and I haven't had an issue with space yet. The SSD is only for apps and whatever I'm currently working on (usually video files), everything else goes to an external 1 TB hard drive that has about 300 gigs of data on it currently.
I think the 27 in with 256 GB of storage is the best bang for your buck that Apple currently offers. External storage is cheap and 256 GB of storage is more than enough for most people. In a perfect world, I would've liked to get 512 GB of storage (to help future proof a little more), but the pricing on that didn't work for me.