We can't hardly answer the question. There is too much blur in definitions on CAQDAS. So you should rather ask: For my purpose XYZ (please be precise and detailed on that), what is a suitable software.
I'm not sure if they're the best, but I've used both Atlas-Ti and NVivo to analyse interviews, and both work well. You can download a trial copy of either of these to test out their capabilities.
Thanks Nick and Romulo: much appreciated. Yes, I would love to get NVivo licences for my undergraduate students, but we can't justify the expense, sadly.