I see the OP has never come back and responded, but out of amusement I'll comment anyways... :-)

The style of carrier you get is largely about how much extra effort that it's convenient to go to to carry your groceries.

The "folding basket" type's main advantage is that it's fairly easily always on your bike, without being a big theft target. No need to remember to bring it - it's just there. But you have to arrange your groceries in such a way that they won't tip over the bag or fall out on your way home.

I wanted relatively affordable panniers that I wouldn't have to worry about stuff jumping out of if I went over some bumpy road. And - and this was critically important :-) - I wanted something that a Dijorno frozen pizza would fit into. :-) So I bought the Banjo Brothers market pannier -
http://banjobrothers.com/products/cu...arket-pannier/





It's:
- Big enough for frozen pizza
- Has handles, you can carry it and use it for your shopping, and also for your grocery bag
- The top folds over the groceries, so nothing is going to jump out of the bag if you go over a bump.
- Likewise it's self contained (no open parts once you fold the top over), so no need to be to neurotic about how you pack the groceries in it.
- It has a pouch on the inside where you can put a rain cover (I bought mine from Calhoun Cycle - the rain cover might have actually been from a different brand)

Drawbacks are that it can only carry so much (2 grocery bags worth of groceries, you could maybe also strap something to the top of the rack, carrying more would require a front rack).

A trailer will definitely carry everything. It's drawbacks are mainly that you're towing a trailer (so no stopping for groceries on the way home from work, in general). And the trailer takes up space in your apartment garage that's much, much larger than the space taken up by panniers.