If you're going in August then you might as well do London mate. That's the one time of the year that the weather is nice there. London has a lot more to do, especially when the daylight is on for 18hours per day. Bondi Beach will be pretty much redundant in the winter.
Id go London. Best city in the world. Yes im from there so I maybe biased but im proud to be from it and if your going early june to august you'll have good weather, Wimbledon will be on(best tennis tournament there is), there will be music festivals on and we've got the best of them too...V festival and The Reading Festival... Also the world cup will be on. Best time to be in this country as we are football crazy or 'soccer' as you call it and the city will be buzzing. Best nights out, so many famous landmarks and if thats enough...
London got picked for the olympic games!
Sydney has been quite misrepresented in this forum. Someone even said it was a smaller version of London when really that couldn't be further from the truth. Think Australia, not just Sydney. August is our winter, but even in August the lowest it gets during the day is 15 - 16 deg C. Sydney is also very clean and bright compared to the oppressive grey skies and pollution of London. Culturally speaking how many museums do you really want to see? If you want to see museums then go to London. If you want a laid back lifestyle in an economically buoyant city then come to Sydney. 1-hours flight North of Sydney is Queensland. They don't have a winter. I imagine you will want to travel after your internship (how long are you planning to stay in your internship for?) and when you do you you'll be glad you came to Oz. The nightlife here is as good as anywhere I've been in the world, and cheaper. London might have 18 hours of daylight in Summer, but you can bet that 16 out of the 18 are wet or overcast. And because you're doing an Internship in an Aussie company you'll meet loads of Australians. Oh, and our takeaway food is fresh, good, and cheap. English food is still in the middle ages.
I'll be doing the internship for 8 weeks and likely living with a host family for the duration of the internship. After those 8 weeks, I'm not sure what I'd do if I wanted to stay and travel some (which of course, I'd love to do). I guess hostels would probably be the best bet. Right now, it seems like I really can't go wrong either way. I think the deciding factor is going to be price, as the internship program is about $4000 (this includes lodging and the host family will more than likely provide meals, as well). I will be responsible for travel expenses such as airfare (which is going to be incredibly expensive), getting around in the city, etc. I do know that the dollar is incredibly weak against the pound right now and that London seems to be a very expensive city. I do appreciate everyone's opinions and advice, though...hopefully I get the money worked out and I can tell you all about it!
I live in Sydney (born and bred), but I have also spent a few years living in London, so I've seen a lot of both cities.
I honestly think people are kidding themselves if they think that Sydney has more to offer than London, they are in a completely different league from each other. It's like comparing New York to, say, Munich.
This doesn't mean that Sydney has nothing to offer, it's just that London has a whole lot more.
They are two very different cities, so it depends what you want.