I've been looking at getting a powered PA Speaker to use with my POD. I'd like to use it for band practice as a monitor on stage so it needs to be loud enough for that. Basically needs to compete with a normal guitar amp. I've seen powered speakers ranging in wattage from 60 up to 500 and stuff and I'm confused how much exactly I would want to aim for. If I don't really need to splash out on 500 watts then I'd prefer to spend the money on something lower wattage but better quality. In case you didn't know I am clueless on what wattage even does here.

Also if there's any suggestions of speakers please go ahead. I'd really like something that looks good too.

Edit: Also is there any advantage to having a 15" speaker over a 12"?