Laser or IPL for fair skin, dark and coarse hair on bikini line, which would be best? Which is less painful?

Great question. There are so many lasers and IPL machines being used for laser hair removal-- is there a difference in pain and effectiveness? The answer is a slightly complicated no and yes... I will answer both as a physician and user of LHR, having had many treatments with many different devices in different areas of my own body.
First pain: pain is related to the sensitivity of the area of the body (for me face does not hurt hardly at all, underarms a little bit and bikini a lot!) and settings. You turn up the settings on any device, it will hurt more. You turn them down, they hurt less but are less effective. I have demoed various IPL machines and many different lasers. One alexandrite laser was shown to me as "less painful" but that one was just as painful as any other. The bottom line is that hairs burning up are painful when this happens in a sensitive area and less so in areas with fewer nerve endings.
Second effectiveness: They all work well when you have dark hair and light skin. They ALL have to be turned down when you have darker skin, and most you must not use on very dark skin. Most clinics do not have an Nd-Yag laser for hair removal-- but that's the one you need if you have very dark skin. But if you have light skin, any will work well.

Lucky you! Your skin and hair type make you an ideal hair removal candidate - pretty much any laser or IPL should work well. For your hair/skin, since both will work, it is more a matter of the clinic. All lasers are not the same and ditto all IPLs - you can have a very inexpensive, old one of either or a new, high powered one. It is also very much dependent on the skill of the operator. Bad hair removal is dangerous, so for this, really do look at reviews and experience of other patients to guide you.