to make some DVD's to play on a regular DVD player. Footage taken off a digital camcorder.

I'm tempter to buy the +R as they are slightly more expensive, so I'm thinking they're maybe better quality. So what's the difference? And why are both types available?

my pc can record either type

I recall going through this myself previously. I eventually decided that -R was the more common choice on DVD players so use that. But I think you will find that most DVD players (if not all) these days can handle both. (-R may be cheaper because it's more common perhaps?) (I may be wrong on all counts though).

AFAIK The two systems exist simply because different manufacturers chose different formats in the early days.

It may depend on what you intend to use to play your discs.

-R is the earlier format, therefore anything which plays +r will* also play -r.

Where you have a device which will play both, the +r is probably the better choice, but it won't be as portable as -r.

*In some closed systems only one disc type will work; e.g. AFAIK the Xbox 360 will only read +r discs.