I'd use a step-through if I had room for one. Perfect errand bike. My usual errand bike is a long wheelbase comfort hybrid with sloping top tube. Not quite crank-forward/flat-foot, but comfortable with a fairly heavy load including a 20-lb jug of cat litter strapped across the top of the rear rack. The spring suspension fork adds enough weight to keep things balanced with a heavy load on the back. And it feels very stable even when the load isn't perfectly distributed.

At the moment my usual errand bike is chainless -- it needs two chains spliced together, about 6-8 links longer than the usual 116 link chain. I bought the replacements last week but was so busy leading up to the holidays I haven't had time to measure and splice the new chain after removing the old chain and cleaning up the bike.

So yesterday I attached the grocery panniers to my rigid fork mountain bike with horizontal top tube. Urk. Felt weird. The balance was completely off, and the usually light front end felt like it was gonna wheelie any moment. With the bike loaded I couldn't easily sling a leg over the top tube, as I usually do with the other bike, or over the stuff loaded on the rear rack. Had to tip the bike toward me to hoist an aching hip over the bike, and nearly dumped it in the process. Then while riding my heels kept hitting the panniers -- practically had to pedal with my heels.

Yeah, I'd find a good use for a step-through.