I wash all lettuce I eat no matter how I received it. I chop it up, then wash it in a strainer then lay it out on paper towels and pat it dry and sort of look it over then put it back into water to soak to crisp it.
I feel very guilty about it because it's a waste of money and of resources (the plastic it's wrapped in, the ridiculous processing...), but I buy bagged lettuce. The fact is, I'm lazy and tend not to eat lettuce if I have to prep it myself. I rationalize that it's more cost-effective to spend more money on something I'm actually going to eat, than to "save" money on something that will rot in my produce bin.
I can't do the smell of bagged lettuce (I'm beginning to think I am a "super smeller"), so I do heads of lettuce. Once in a great while, I'll get a bag of the butter lettuce which I can't detect the bagged lettuce smell. I love butter lettuce.
I do the big plastic container of spring greens. I get it either from Costco or Shop Rite. It stays fresh for a week, and I use it for my lunch salad every day. I heard the bagged salad goes bad a lot faster, and I can't stand when it gets that rotten smell. I've had good luck with the greens in the hard plastic container staying fresh- I hardly ever have to throw any away. Oh, I don't wash it either- it says prewashed, and I'm the trusting type.
I HATE lettuce! BUT...I eat it for taco salads. That said, I only buy the red head lettuce-not in the bag. I can't stand that it comes in such large quantities because I end up wasting almost all of it.
I prefer the head lettuce but time constraints and my degree of laziness frequently prevents me from purchasing it. So most of the time I buy the bagged. I guess I am trusting I don't wash it and have lived to tell about it.
We buy almost all of our Romaine lettuce at Costco. The bags usually have 5 or 6 heads of lettuce in them. I always wash all lettuce even when it comes out of my garden. My garden lettuce is washed to get the slugs out but no worries about pesticides or other contaminants.
Bagged - or actually plastic containers. We bought large bags of lettuce mix from BJ's for years but with no one really home much now, it was going bad before we got halfway through it. About 3 or 4 months ago I started buying the plastic containers of spring mix (actually the one I bought yesterday was called 50/50). Like Munchkins said, it lasts about a week. I know we have a lot there so I make myself eat more salad at dinner. I don't wash it either.
I do both. When I have more time or if I'm making burgers/sandwiches I'll buy the whole head of lettuce, otherwise I buy the precut stuff. EVERYTHING gets rinsed. I can smell the wash on the precut stuff, so I have to wash it off.