Best thing to do is try to look through each, preferably side-by-side. The ergonomics are quite different, but both are great glass. NLs are considered the best on the market, if that's your thing.
Biggest difference is the field of view. Comparing 10x EL and Pures, the Pures get you almost 20% more country in your field of view (measuring at 1,000 yards). The 2 benefits to the larger field of view (to me) are 1) more likely to pick up animals (esp. when using a tripod) and 2) the larger field of view makes things appear more steady when handholding.
I compared for a good amount of time 12x42NLs and 12x50 Els.
I thought they were nearly identical. FOV of NLs maybe a shade bigger (less than 10% actual not provided #s).
I think the eye relief and placement forgiveness were better with ELs (makes sense bigger exit pupil). I get a bit of blackouts internally scanning with the NLs.
Biggest difference is weight and ergo. Especially in the 12x. It was worth the savings for me.