Which is best?

for me:
http://www.currys.co.uk/gbuk/lg-e2351vr-bn-23-full-hd-l...

first of all 5ms response time not good, but better than 6ms.

23 is the minimum size for me; 21,5 is getting to small already;

full led backlight is good (not sure if the first one also is full array);

I've had a ton of issues with LG monitors, look for Samsung or ASUS. Even ACER or HannsG may be better. Don't worry about the response times, contrast, etc... manufacturers almost never use the "correct" way of measuring things. One monitor at 8ms may be as fast as another rated at 2.

Read online in-depth reviews or customer reviews from the store.

You can't really purchase a monitor based on numbers alone, just like a car or a dinner. Would you go to a restaurant just because one place serves larger steaks and not care about how they cook it?