Which phone is never hang?

If you can handle widows phone then you should go for it because WP rerely hangs unlike Samsung which hangs too much even with 645mb of ram. But you can see Nokia lumia 520 with 512 mb of ram it does not hangs on a normal use with normal apps like whatsapp fb etc.

Do Samsung phones still lag?

To prevent this lag in Android phones, Samsung uses more RAM and CPU speed. However, a RAM and CPU loses their computational efficiency over time. So, when a new Samsung phone comes out, it runs smoothly. Yet, after 12-18 months later, those same Samsung phones struggle to run apps without lag.