Have been travelling non-stop for 6 years now, in all parts of the world, and wouldn't consider anyting but a hard sided suitcase. I currently have one of these in turquoise:

http://www.amazon.com/Samsonite-Lugg...JMI/ref=sr_1_1

Reasons I bought it:

1. Hard(ish) shell: I previously had a soft-sided suitcase, and it was ineffective at protecting the contents from damage.

2. Catches rather than a zipper. I hear modern zippers are a lot better than they used to be though.

3. Combination rather than a key.

4. TSA compatible lock.

5. The top shell is thinner than the bottom, making it easier to leave open on a hotel luggage stand.

6. Two fairly large wheels, making it easy to roll over cobblestones in medieval European city centres and unpaved paths in developing countries.

7. Two wheels. Every time I see a four wheeled suitcase, the wheels stick out a lot, and give the impression of being easily broken off by clumsy baggage handlers. Maybe I'm wrong on this, though. B&R's lifetime warrenty would alleviate this worry.

8. Unusual colour so I can spot it easily on baggage carousels. I've lost count of the number of times I've seen someone pick a black suitcase off the carousel, only to put it back when they realise it's not theirs.

9. Unusual colour to deter theft. Apparently thieves like to walk in to the baggage hall (where they can), take a generic black suitcase off the carousel, and walk out with it. If confronted, they claim that they thought it was theirs as there are so many similar black suitcases.

10. 30" is about the biggest size that all airlines (even bush airlines in Africa flying Cessna Grand Caravans) will take.

However, it has the some disadvantages:

1. I used to fill it up, but I carry less than I used to. These days, it's only about 3/4s full. This means wasted weight I have to carry around for no reason.

2. Whilst airlines are happy with the size, 30" is just a little bit too big for some car boots (trunks for Americans). In particular, Hertz like to upgrade me to Mustangs. The hard top Mustangs are fine, but it's just slightly too large to fit in the boot of convertible Mustangs. The boot itself is probably large enough, but the hole is slightly too small.

3. It's a little too big for some hotel luggage stands, which means it has to balance just on the edge and risk falling off.

4. It's a bit of a nuisance to carry on trains. This is particularly true on Indian trains, where the main storage is under one's seat, and the 30" is a few millimetres too thick to fit.

5. It's not quite as well built as the previous hard shell I had (whose brand and model I never did discover, as it had no labels of any sort). In particular, I put a large cloth bag of dirty laundry in for one flight, and the pressure of this pushing against the internal mesh divider managed to pull the self-tapping screws holding the anchor point for the mesh out of the hard plastic shell of the case. I successfully repaired it by replacing the screws with slightly larger ones, but wasn't too impressed.

I'm thinking about trying a four wheeled suitcase next. The large B&R Torq looks close to ideal (except perhaps the thickness), but is not out yet in Japan and Europe (which is where I've been recently). I'm waiting to see what it's like in real life before deciding. The alternative is the Tumi medium packing case, though this may be beyond your budget.