So which is better a lockup converter or a non lockup. It's being put in a Chevy 4x4 with a 700R transmission, it's a daily driver and used for towing?
If you are going to be towing, you want a lock-up torque converter. Heat is the bane of transmissions. Towing will add heat to the transmission. A non-lock-up torque converter will add more heat. With a lock-up when you get to speed, the torque converter will lock-up, which creates a direct drive from engine to transmission. No additional heat will be added into the tranny fluid due to slippage during operation. This will help extend the life of the transmission.
You'll also want to consider putting a large external tranny cooler on your vehicle. This does two things. The obvious one is keeping the transmission cooler. The second thing it will do is adding more transmission fluid into the mix, which will usually allow it to last longer. The transmission cooler which is located in the coolant reservoir is not up to the task. Bypass this all together as it will not provide any additional cooling which the external one won't cover.
The 700r will only lock in 4th gear. This can be hacked for towing to manually engage in 3rd, where most heavy towing is done. http://www.hotrodders.com/forum/700r4-3rd-4th-lockup-102313.html
The main reason lock-up torque converters were introduced was for “parity” with manuals to try to match or, at least improve, the fuel consumption when cruising.
This was also combined, in some cases, with an “overdrive top” again for the cruise performance and the top end speed.