Thy cheapest one ...
If you are looking for the least expensive code 83 flex, go for the Atlas. However, if you want the nicest quality code 83 flex, consider Shinohara.
Both are good products. The delta in price between your Local Hobby Shop and the Internet, after you pay for shipping is not that much. For example, today I bought 20 39" sections of HOn3 Shinohara, joiners, spikes, various straight length and radii track laying gauges (A MUST for any flex track) and paid about 10-15% more than I could have on the internet.
Why? Because for the extra $20 they provide me a wealth of knowledge so I do things the correct way - I trust them. Do I buy everything from them? No, but I do give them quite a bit of my business. Good relationships are priceless.
Dog
"Some people know the PRICE of everthing and the VALUE of nothing".