Besides my Passport, there is no object I love more than my suitcase. I only have one, and it was given to me as a graduation gift ("Oh the Places You'll Go", but in an object, instead of a book.)
Anyhow, I wasn't given the opportunity to select it myself, but it's still one of my favorite things.
Steps for finding your suitcase soulmate:
1. Pick a size that you can carry on your own, if it was full of hardcover books.
i.e. it should be small.
This is the number one, most important rule. ALWAYS pack light. You can purchase things you need along the way if you have forgotten them, but 9 times out of 10 you won't use everything you packed. You should be able to pack for most trips (2 weeks or less) in a carry-on, and without stuffing it. Overpacking, unless you're Anna Dello Russo, makes you look like a novice. At everything.
2. Consider where you travel most often. Business travel requires a much different suitcase than a casual holiday traveler. A ski bunny needs luggage that would be wrong for a weekend in Bahia.
3. Organizational Opportunities.
i.e. multiple pockets
4. Aesthetics and Price
Here are my pics for luggage that fits all the criteria for numbers 1-3. For criteria 4, the beauty is, it's entirely up to you.
This is the suitcase I have. While its not the distressed leather beauty of my dreams, it is really practical, and really light. It also can be rolled, or thrown over your shoulder with added backpack straps. It's also really small, but fits a lot. Highly recommended.