Speedbird,
I've done both, so probably in a good position to compare them. What I did was more in the name of having fun than hour-building, but there was certainly an hour-building element to what I've done too.
Advantages of going to the US: Good weather (assuming you choose somewhere appropriate of course). You get exposed to a different flying environment. There are also advantages that come from the fact that you're renting - you can try out lots of different things. In two months, I flew a Warrior, did a tail-wheel conversion on a Super Cub, a complex converstion on an Arrow, some twin time on an Aztec, some aeros in a Great Lakes, and also had a go in a Pitts Special - you can't get this kind of experience by buying your own aircraft because you'd be reluctant to fly anything other than the one type that you've bought.
Advantages of buying: You get a sense of ownership. This makes a real difference to the way you fly. It suddently seems far more practical to go away for a few days, or to make a last-minute decision to go flying when you see blue skies. The ownership lasts past the hour-building, so hopefully you will enjoy flying your aircraft for many more years even after you find a commercial job. You get to know your aircraft intimately. You can buy any obscure type of aircraft you fancy rather than being restricted to what your local club has on offer. There are few disadvantages of this route, though: lots of money needed up front (although you can get this back if you decide to sell), as well as all the other costs, hassle and potentially down-time that come with ownership.
If you're planning on doing 50 hours per summer over three summers, I'd suggest spending the first summer in the US, then buying a share in something in time for the second summer (you'll need to start looking in the New Year - you definitely don't want to rush into buying an aircraft).
Hope that helps,
FFF
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