The ability of transferring very large files in the shortest amount of time is crucial for data-intensive Grid applications. Experimental evidence has shown that the mere availability of high-capacity wide-area networks is not sufficient to obtain adequate performance if vanilla TCP is used to transport data. Consequently, many alternative solutions are being explored, and a variety of data transfer tools have appeared. In this paper we experimentally compare some of these tools in various network scenarios. Our results show that solutions based on UDP, adopting rate-based algorithms, result in better performance than other alternatives in most cases, while solutions based on TCP are effective only under specific circumstances.