Which resistance band to buy?? Links included

I know absolutely nothing about resistance bands but someone suggested these for me on my last post and I'm not sure which of these I should buy!

http://www.walmart.ca/en/ip/bally-14x-training-band/6000107232863

Or

http://www.walmart.ca/en/ip/resistance-tubing-set/6000077045543

Or maybe just one of these: Not sure if light, medium or heavy would be best?

http://www.walmart.ca/en/ip/everlast-ultimate-resistance-band-medium/6000108577817

Thank you!!