QUOTE(sjneow @ Sep 16 2015, 11:16 PM)
yup, 640 XL is the phone that perfectly fits your requirement. it matches all your bullet points except maybe for single sim. there are single sim 640 xl, but Microsoft main production line focuses on the dual sim versions of their phones, so single sim is harder to find.
If you are concerned of sim card detection problem you should be pleased to note that windows phone boots up and detects sim card very quickly, so there is no drawback in taking the dual sim version at all.
btw, windows phone has excellent camera app that makes low mp camera takes comparable or better photos than Android phones with higher mp. So you will be blown away by 640 xl's 13mp camera.
Outdoor picture are superb. No doubt on this but you might be struggling with indoor/low light.
The flash is also consider not very bright for dark environment.
QUOTE(weichai @ Sep 17 2015, 01:23 AM)
There are 2 models, lumia 640 XL 3G & Lumia 640 XL LTE.
which model is nice & suitable for use?
Thanks.

If you can spend a bit might as well take the LTE. Consider it future proof in case you upgrading your data.
If you are a gamer, don't pick this phone. The hardware is just to average to run games and Windows Store have limited choices of exciting games. Also some of the popular apps sometimes are in beta, eg Instagram and some no longer updated (Waze etc).
Overall it's value for money but it's really depends on users.