Hardwood! Carpet can get disgusting. Our next house will definately have harwood in the main areas/carpet in the bedrooms is fine. Ceramic tile or vinyl that looks like tile in the bathrooms and laundry room.
I love hardwood floors and had them in my house in Utah, but here in So Cal the trend is tile and we have a lot of tile! It certainly isn't as warm as wood, though. I have a friend who recently put bamboo flooring in her home and it looks fabulous (just like wood--well, I guess it is a type of wood!).
Hey, if your mom is selling your Gramma's house, you may not want to invest in hardwood. Most buyers out there want a home that is absolutely clean and fresh. For the cost of hardwood, you can replace the carpets with new, neutral ones that aren't too expensive and repaint the place to boot. Some say that hardwood is a selling feature, but it really depends on the room and the type of hardwood -mid-tone oaks are out of style, dark wood is somewhat overdone, and trends are towards lighter woods. You might turn off a buyer if you offer oak floors and they want bamboo or natural maple or stained-coffee colored ones. A buyer will look at oak floors and say, boy - what a shame, I hate the color and what a pain to replace them with the bamboo that I want. They will look at a brand new carpet and say, boy - what a shame, but the carpet is new and we can save up to replace it with the bamboo flooring that we like in the future.
If I was to LIVE in the place, I would prefer hardwood. If I was buying a place and the carpet was new, that would be fine, too. If the carpet is OLD, forget it! That is a real turn-off. So is laminate flooring in most above-ground locations. While I have it in my place, UNLESS it is done really, really well, it tends to tell a buyer that you've gone on the cheap. (I expect a ton of hate mail for that, but it is TRUE, from a buyer's persepctive). The same goes for vinyl linoleum, press-and-stick tiles, and wood-tone vinyl flooring. Parquet flooring is an option, and preferable to laminate flooring at about the same cost, but again this option isn't generally well liked by the average buyer.
SO, go for a nice, not too expensive, sisal-type (i.e. low pile) neutral carpet, with an OK underpad (don't go nuts with respect to $$$), and you should be fine.
My vote - hardwood or Pergo type floors called laminate flooring I believe. I don't like Pergo brand itself but had my house done with Aalco(sp?) brand floors and I LOOOOVVVVEEE them. No more vacuuming. Just a swifer dry and wet is all you need.
As someone who grew up with asthma (and DH never out grew his) I'd say hardwood. New carpet will off-gas VOCs and carpet gets gross really fast. Even if carpet looks clean it most likely isn't. I would be a lot more willing to pay a higher price if the house had hardwood versus carpet, but neither would be a total deal breaker (one way or the other.) Flooring is an easy thing to replace.
One of the reasons I bought my current home is for its beautiful oak floors. Wall-to-wall carpet is harder to clean. It harbors all sorts of dust and allergens. For me, wood or high-quality linoleum (the kind where the color goes all the way through instead of just on the surface) is the way to go.
I much prefer hardwood over carpet..and I think the majority so. You've got people with allergies who can't take carpeting, and even if you prefer the carpeting it's perceived (and rightly so!) as being less sanitary/grungier than hardwood. Hardwood looks classic and modern at the same time. It goes with everything. Super durable, super easy to keep clean.
My current home is completely hardwood (although it does need to be refinished!) and when we build our next home I told dh its totally hardwood with tile in the entry and bathrooms..he says laminate When is he going to clue in that I'm the boss?
These days, hardwood floors are all finished with polyurethene, which is very hard to damage. The hardwood floors from a couple of decades or so ago were much harder to maintain, but that just isn't true anymore.
Ahhhh well then that clears up my biase towards hardwood. I lived in an older rental property with beautiful hardwood cypress floors.. Which upon close inspection were really nasty. There were cracks between the wood panels which had collected years of dirt, they were scratched, and part of it was discolored. I don't think they had been finished properly or something, because they were a pain in the butt!!
Now my new house (built in the last two years) has some sort of non wood flooring, which is just finished to look like wood (not sure what the heck it is but it looks great and is so easy to clean up), coupled with ceramic tile in the kitchen and bathrooms. There is carpeting in the bedrooms which I haaaaaate. It stains so easily, and since I have physically pulled up carpet and seen what lurks underneath, I know it is NOT pretty.
When is he going to clue in that I'm the boss? 
