I've owned hamsters, guinea pigs, rabbits, gerbils and rats, and also have a close friend who's had mice and a degu, so I feel like I've 'sampled' quite a lot of the most common rodent pets. And I can honestly say that rats are one of (possibly THE) best ones of the lot. Over the past few years I've had 8 rats and I've had experience with both males and females and I think they're wonderful!
It makes me kind of mad now when I'm in the local pet shop and I see parents getting hamsters and rabbits for their kids, because everyone chooses hamsters and rabbits and (for kids at least) they're two of the worst pets to get for them! Hamsters are a favourite with a lot of people but can be really awful biters while rabbits are lethal once they start kicking!
But back to rats :) All the rats I've had have been friendly, lively and very interactive pets. Pros are that they are more intelligent than hamsters and things, and will learn to recognise you, be pleased to see you, and generally be more interactive with you specifically instead of just wandering around like many small rodents do. In fact they can even be trained to respond to their names if you have lots of time and patience!
Rats are good because they're active during the day when you want to play with them instead of just when it's dark like some other rodents. In the wild they're omnivorous opportunists rather than prey animals like many rodent pet species, which means that they tend to be less skittish and nervous and more inquisitive and interested in what you're doing. They're also good climbers, which means you can let the rat(s) sit on your shoulder or in a pocket while you walk around and he/she is unlikely to just fall off.
Female rats are very lively and curious and enjoy exploring and crawling all over you, whereas the males tend to be more lazy and laid-back and prefer to just snuggle and snooze on you. And you can keep either gender in pairs, so it's up to you if you want 2 males or 2 females.
To be fair, I'll add the few 'cons' I've noticed too. Firstly, they do smell pretty bad if you don't make sure to clean them out regularly and give the cage a proper scrub each time too. Males (unneutered, at least) smell worse than females.
Secondly, they require a larger cage than hamsters and things since they're bigger and also need more mental stimulation, so they need lots of space to run around and lots of toys to keep them occupied.
The only other 'bad' thing about them is that they're especially prone to getting tumours as they grow old, which is pretty sad and can get nasty if untreated. Quite a few of mine ended up being put down when they got old and developed tumours. But it's hardly their fault they have health risks, and it would in no way put me off of owning more of them, since they're wonderful little animals. :)