Peco vs/ Atlas
Peco track is made in the UK, and as others above have noted, the price is higher than Atlas and varies a great deal. Try some UK stores, if you buy enough the shipping cost would be well worth the price savings over most US sellers.
Track vs. track: the Peco is in my opinion, better made with more realistic detail; however, the plates and details are European prototype in nature. The concrete tie flextrack is outstanding, and I do not believe that Atlas has anything like it.
Turnouts vs. turnouts: no contest, the Peco are true, positive locking, and work very well with Tortoise switch motors. I've never hade to file the points on Peco switches; Atlas switches, depending on which plant in China they come from, require lots of tuning, in my opinion. However, you pay for that quality - about 55% more for the Peco. (Same observation regarding the details at the tie/plate level as noted above.)
And if you run European prototypes rolling stock and engines, then the extra depth of the Code 100 Peco will give more than adequate clearance for the rather large-flanged NEM equipment. I've had a lot of rolling stock that won't run across Atlas turnouts without a lot of work on the frog on the turnout with a Dremel tool. (To me, not having to perform that work effort is worth the premium price for Peco.)
David