I've been using Topeak trunk bag, but with winter, I'd like the added flexibility of panniers. I have a grocery pannier (Avenir), but had heelstrike problems, and had to drill new holes, and move one of the hooks about an inch. Now I'm fine with it. Can I use this information to pick more traditional panniers I won't have problem with? Is the grocery pannier design more conducive to heelstrike? Less? Can one draw broad conclusions like that? I haven't seen much selection at any of my LBSs, so I anticipate purchases being online. Can't try them out first.

There are a large number of variables that can contribute to or relieve heel strike, including: shoe size, crank length, chainstay length, rack length, pannier size.

Good info can be found here https://bicycleluggageracks.com/

Check out his sections on long racks and wide panniers, as well as shifting.

When I made the move to panniers a bit over a year ago, I found I had to slide the panniers back a little over an inch to get rid of heel strike. Wasn't a big deal and has worked great every since.

Rectangular panniers are also worse for heel strike. Unfortunately ones with angled fronts usually cost more.

Also panniers come in different sizes. Perhaps you need smaller ones?

Adam

If it is a problem, hang the panniers as far back on the rack as possible and find a way to adjust the panniers further back. (I ended up buying adjustable touring racks - that could be adjusted for height and distance from seat post)

Yes.

A pannier with a profiled heel cutout shape (eh carradice Super-C) will help this problem.
Moving the pannier back will reduce heel strike but will transfer weight behind the axle. This can have effects on bike handling when very heavily loaded. The bike tries to tip back, lightening the steering and generally getting unstable.
A profilled pannier allows you to maintain more weight within the wheelbase.

I'm not sure why this is, but I get heel-strike on just about any pannier I put on my bike... at least for the first 1/4 mile. Then, somehow I make an adjustment, and everything is OK.

There are two adjustments: 1) kick the pannier hard with your heel so it moves back at bit; 2) angle your foot a tad so it misses the pannier.

Having said that, I have a number of pannier bags that look scuffed up on one side. I guess I have it adjusted so my heel just barely grazes the bag.