I get asked this a lot. I'm pretty sure the initial answer I give is not one that people are looking for. My answer usually starts with "It's the camera you have with you. Because really, you can't capture anything if you don't have a camera with you."
Don't get me wrong, I love my "big" camera (Canon 5D Mark ii) but I also love my little walk around, underwater camera (Olympus Tough) and my even littler iPhone camera. And, full disclosure, I would love to get my hands on the Mark iii!)
Although better gear can give you more flexibility, it doesn't necessarily make you a better photographer, and in some cases, might stifle your abilities if you aren't familiar with or afraid of the vast array of possibility that a DSLR allows.
So, when the pull of desire for new equipment comes calling, sometimes I challenge myself to create compelling images with the Olympus or iPhone. It reminds me that I can still create appealing and meaningful images no matter what camera I use.
What are you going to shoot today?