If you can lay your hands on free glass, then that's always the best way... but you have to know you can get the glass when you'll want it.
Personally I seldom shoot under 70mm, and when I do want more, I desperately try to use my 150mm 2.8, but for certain occasions I need something more flexible, and that's where Lenses for Hire come in. I've just rented a Nikon 70-200 f2.8 for our year 8 school prom in a months time... something I'd dearly love to buy, but I just wouldn't use often enough to warrant the £1,500 price tag (yet anyway).... £65 for a top lens though... that's more than acceptable.
Really it depends on what you want to shoot, but don't eliminate what might be your ideal product just because you might have access to good glass on another system. If you expect to use a multitude of lenses, then you need to know you can get them. If you generally shoot short or long then want something else occasionally, then hiring might be a better bet, if it means you buy into a system that you're more comfortable with. Of course, if that system happens to be the one where you can also get access to good glass for free, then it's win-win.