Not going to pull the trigger until next year, as I've already got my toy budget used up, and my current 2012-era Mac mini quad core is going strong, maybe my favorite Mac ever.
But at some point, it'll be the i7, base RAM, and 512GB SSD.
-- I'm a developer, as a pro and as a hobbyist, so threads matter. Ordinarily I wouldn't throw down the extra US$200 to get a seven-percent boost in clock, but the i5 hexcore is six threads while the i7 is twelve threads. Plus maxing out the CPU is pretty central to future-proofing, and I'd want to hang onto this thing for a while.
-- Base RAM. It's interesting that Apple broke their own if-it-moves-solder-it-until-it-doesn't rule here, and I think that's a sign that they're doing a better job at getting their head around the headless desktop. Upgrading the memory later helps me spread out the cost of the machine. Soapbox below.
-- I've already started moving the more graphics-heavy development stuff to my unextravagant gaming tower with a GTX 1060 (and an Ubuntu partition on SSD), so integrated graphics on a mini is enough for now ... in the sense of, well, okay, I'll need to pick up a 4K monitor too. But the genius of the Mac mini is that if it blows smoke, I don't have to landfill a perfectly good monitor too just because it's been welded to the computer. At some later point, I may consider an eGPU, but I'm undecided on the wisdom of muscling up a Mac to the point where it's on par with another machine I already have, and I want to see how the eGPU thing shakes out in general. The nice thing is, I don't need to decide up front.
-- There's a speed difference between internal and external SSD, and since I'm presuming I won't have a chance to upgrade it (which as I understand it is one of the ramifications of having a T2 security) I'll bump it up a notch but not to the skies. If at some later point I need more, I can move some lesser-used things to a still-fast-just-not-quite-as-fast external SSD.
Soapbox:
I think Apple under Tim Cook went badly awry on the headless desktop, followed their own dreams without regard to the pro market, emitted a row of platypuses with tap shoes where Macs used to be, got spanked, and went back to the drawing board. True with the Mac Pro, but also true with the Mac mini. They didn't know what people used the mini for, and read their own press about how it's only an intro/switcher machine, and killed the quad core. Bringing it back is a tacit admission that, whooops!, we misread the market in 2014 and did a dumb thing, and then nattered in confusion for a couple years, and then realized we'd better bring back the essential mini now that we understand it. And their having put a couple of USB-A ports on it is a nice concession to actual reality, which is that we're not all worshiping at the Church of the One True Port, and that USB-A will be the standard for keyboards and mice and lots of other peripherals for a long time to come.
Having said that, by moving the mini up the performance spectrum, they've made me happy at the expense (literally) of those looking for the rilly-low-cost switcher machine. They still haven't worked out that the mini is two machines -- the workhorse I waited for, and the entry machine they used to make. I can't even argue that the iPhone is now their entry machine, as clobbered the low end on that one too when they killed the SE.