Buying would be a better choice for me. Home-owned steam cleaners sell pretty well, and I've seen a lot of good reviews on various makes and models, so I don't believe they won't work. Especially on a fresh spill, they should work just fine. And that's what I want it for: Fresh spills (as I said before). When I have something to clean up, am I really going to go hop in the car to the local supermarket, hope they're not all rented out, pay $40, lug it home and lug it back? I don't always have forty dollars in cash handy, and by the time I get it back, the spill will have turned into a stain. And, within about three months, I will have spent more on rentals than I would have on a very good home steam cleaner.
My sister can attest to the condition (and colors) of the carpet in my previous apartment. If my sister can tell me that, in her opinion, I don't need to worry about trying to clean up spills and messes the instant they occur, then I'll consider it.