I've seen this asked so many times and I've often wondered it myself. I've always thought I had a pretty good understanding of it, however I've been described as being both before by different people to the point that it really is up for personal interpretation.
I used to hear girls talk about Zac Efron being cute. Don't hear it that much anymore though. It's the image. Cute is more childlike, warm, fun...Might even fall into the category of a "nice guy". He's caring, approachable, friendly, and an all round good guy.
But now? Girl's might refer to Zac Efron as being hot. He's got a completely different image. It's the 'bad boy' look; manly, dominant, not as warm as before, to the point of being slightly cold. Slightly dangerous, intimidating, unpredictable...but exciting. Not the type a guy a girl will be dreaming about marrying, but the type of guy a girl will lust over.
The same applies to the ladies. Take Miranda Kerr. Warm, friendly, innocent. Approachable, a good role model, respectable. Typical wifey material. She's cute.
But how about in this picture? Intimidating, far more sexual, definitely not warm and innocent. Role model? Don't think so. But with that being said? Exciting? Yes. More likely to turn guys on? 100%. She's hot.
The simple fact is people can be either, no one is either one or the other. It all depends on how you wish to present yourself. Warm and approachable? Or Sexy and exciting? That really is what it comes down to. Most guys will be happy to be called 'hot', in fact we'll far prefer it to being called 'cute' as cute doesn't coincide with the dominant ideals of masculinity.
Women, on the other hand, often won't appreciate being called 'hot' from guys as they'll consider it as overtly sexual. But the thing is, you choose how you want to be perceived. I'm sure most guys wouldn't call Miranda in the first pic 'hot', but wear revealing clothing and look sexy and people who find you attractive will consider you to be 'hot' whether you like it or not.