The SRAM-7 has an excellent reputation. A fair number of randonneurs use it, and it holds up fairly well under that sort of use. They're also fairly repairable. Shimano hubs do not hold up as well, and aren't as repairable. Some of the parts just aren't available. And Shimano's planned obsolecense means even if the parts *were* available, odds are they're not now. V. depressing.
That said, if you're a "normal" user, odds are you won't wear out a Shimano hub quickly. They do tend to last at least 10k miles if you're not mean to them. For me, that works out to an expected lifetime of about 5 years.