They both offer truly unlimited talk+text, an unspecified data cap (which is reported by people on here to be 2 GB) in which they will suspend all your service (including talk+text) and then boot you off without allowing you to port your # over.
Both aren't forgiving on excessive data, if you want more leniency on data then you go with the T-Mobile sim over the AT&T one.
The only difference between the two is the price: Net10 is more expensive because Tracfone has agreements with pin sellers whereas Straight Talk only has exclusive agreements with Walmart.
Net10 would cost you $46.50 from Calling Mart with the 7% discount that's offered every month, whereas Straight Talk will run you $45 plus whatever sales tax is in your state when you order it on Walmart.com.
You can get the Straight Talk for an even $45 with no tax if you put a New Hampshire or Oregon shipping address at checkout. Pin is emailed to you and not shipped to that address anyway. Walmart should realize that since prepaid is virtual then there should be no sales tax anyway, besides you can get every single prepaid tax free (even Tracfone & Net10) from pin sellers except Straight Talk which is exclusive to straighttalk.com and Walmart.