We've been discussing sometimes with Stefan about what bag is acctually better to grab in the store if we have forgotten to take our own.
Seems that neither bag (link in Swedish) is a good choice.
For making plastic bags oil is used and for making paper bags more resources and transports are needed than for making plastic bags even if the bags themselves are recyclable.
Another interesting fact they presented is that you need to reuse your canvas bag up to 131 times before you are at the same environmental impact level as the plastic bag you use once.
Someone told me though; it doesn't matter what bag you bring to the store as long as you bring your own. I think I'll try stick to that advice, not to make it too complicated and hopefully my canvas bags will last at least 131 trips.