This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: Sharon Pedersen <email@example.com>
This is a condensed version of a longer article on panniers, low-rider
racks, loading and generators. --Sharon firstname.lastname@example.org
Price--cheaper may not be better, if they fall apart. Commuting to
school entails stuffing sharp-cornered books into them thus making
sturdiness as important here as for touring.
Cut--an angled cut may make those books not fit so well.
Pockets--convenient for organization, but cuts down on versatile use
of space. You can use stuff sacks for organization instead of pockets.
One big and one small pocket on each pannier is plenty.
Fastening--lots of options: bungees and hooks, or fixed placement
hooks, or straps with buckles or cams. Bungees and hooks have been
just fine in my own road experience, but for off-road riding, you will
want more security. However, don't get a system with so many
attachments that you can't stand to take the panniers on/off.
Brands--the following is a by no means exhaustive list, with
telegraphic comments made in 1988. Check local stores since features
may have changed since then.
Eclipse--(no comment); Kirtland--tourers like them;
MPacks--panniers made by an actual bike tourer, Mike Center, in
Santa Rosa, CA, (707) 545-4624;
Maddens--made in Boulder, "superior construction at better than
average cost" yeah! (I love mine, write for more glowing testimonials);
Performance--low-cost, non-spring attachment; Rhode Gear--expensive;
Tailwind--aerodynamic, rigid attachment.
Some manufacturers: Bruce Gordon, Blackburn, Vetta, Voyager. The
Bruce Gordons are more expensive (~$70 in 1988) but are designed with
clearance for the quick-release skewer so you don't have to pry them
apart to take the front wheel off.
(No comment in the original article; Blackburns seem to be the
standard and durable enough.)
Balance the load side-to-side and, if possible, fore-and-aft.
Keep heavier items low and towards the bottom bracket. Rider, bike
and luggage together should have 55-60% of weight on rear wheel;
remainder on front. Bike with front low-riders is quite stable.
The usual location on the left seat-stay interferes with panniers.
Mount the generator on the right seat-stay facing the other way, and
it will work fine, despite rotating "backwards." Or go with a
generator under the bottom bracket, which will have the advantage of
putting the wear on the tread rather than the sidewall of the tire.