I've CC'd my 26 and 30 extensively. I use a galco kingtuk for both, big fan of the king tuks, and the 30 conceals quite well on my thin frame (6'3" 185lb) with anything less revealing than a t-shirt. The fatness seems to grab at the fabric and every time I lean it prints bad in a tshirt, but I typically office carry under a tucked button up and the 30 works in that method just as well as the 26. The tuck on a button down keeps the fabric from bunching and I get no printing.
The 26 is still too fat for tshirt IMO, same problem it's still too fat, but not nearly as bad as the 30, so I view the two as very comparable with a slight edge to the 26 on concealability.
I have four main carry styles, and four guns so I can perfectly match each use. 30, 26, LCP, and LCR.
1. Regular day to day IWB, the 30 rules. Great round, great shooting, easy conceal. The only foible is round count. 9+1 isn't a lot of rounds but I usually don't need a lot of rounds. Any time I don't need to IWB with slim fit clothing I like the 30.
2. Deep conceal, the LCP is best. It fits in a pocket, IWB, ankle, anywhere. I mostly pocket and ankle carry it or IWB with slim fit clothing.
3. Pocket carry, the LCR is best. A spotless model can be fired without removing from my pocket. I like the LCR for winter weather on my commute in case I get mugged by a single attacker.
4. Heavy load out, I like my G26 because it uses the standard double stack 9mm magazines, meaning I can CCW my G26 and put my SUB-2000 in my backpack with 3x33rd magazines as backup. This is the carry application I bought my 26 for. I won't discuss SHTF really but for example I carried this setup after the recent WW3 scare in case I saw any ISIS or Hezbollah flags unfurling in a crowded location in the immediate uncertain period following our drone strike.
Overall the 26 and 30 are roughly equal in concealment, but those huge 9mm mags combined with the slightly easier to conceal measurements do give it a slight edge overall. You won't go wrong with either though.
Also worth noting I prefer gen 4 to gen 5. I like the third pin more than i hate the finger grooves. I'd get a gen 4 26 over a gen 5.