Based on my test-drive comparison back in 2008 . . .
XB- better to drive, brakes don't chudder after a "spirited" drive, can actually see more out of front windshield (like street lights), and a MUCH larger, useable rear cargo space
HHR- Looks like an shrunken early 1950s Suburban or Panel truck, turbo version accelerates faster (xb still handles better)
I really, really wanted to like the HHR and tried to convince myself to get one. But, it drove like an econo-box. The B drove MUCH better, in every aspect, had a nicer, much larger interior, a better back seat for the kids, and more. I preferred the Mini Clubman, but it was significantly more expensive and smaller/tighter interior with much more "difficult" access to the back seat.
(And I'm a HUGE fan of early 50s Chevy trucks & panels and the original Mini is one of my all-time favorite cars -along with the Austin Healey 100, Austin Healey Sprite, Porsche 550, Lotus Elan, Morris Minor (and now the Austin A35), Toyota FJ40 Land Cruiser, International Scout, and Willys Jeep.)
I was also looking at a used black 2006 Mazda RX-8 with paddle-shifters, for about the same price a the B. That was a CLOSE toss-up.
I spend my money on the xB-> best balance of driving, more adaptable/best cargo room, and most "liveable" one of the bunch, and the most cost effective for what one actually got.
I haven't regretted my decision. The ONLY things I've EVER second guessed were:
Color-> I LOVE the Stingray color, but it wasn't out yet and the color samples they showed me looks like an odd shade of blue. So, I got Silver (with the idea of, eventually, painting it and the remaining exposed silver would look "metal").
Transmission-> I got an auto for 2 reasons: my wife thinks she can't drive stick (she can) and the "similar manual" I test drove wasn't very good- being sloppy and imprecise. Since then, I've driven and xB manual and it is a GREAT manual.
That said, I do enjoy my silver auto. The s-mode (or whatever it's called) almost makes up for the manual advantages.
Thus, my B beat out an RX-8, Mini Clubman, HHR, PT Cruiser, and others to be the one I bought.