Best new phone under 20000 is, Honor 4C, Lumia 640 dual sim, Lumia 640 XL.
For 1GB RAM ANDROIDS, which are mostly under 20000.
1GB ram Androids usually have lagging issues, mostly because of installing too many 'social and IM apps'. Other than these, they work very good and fast.
I am using stock 1GB ram Android phone with minimum possible 'Social and IM apps' and 150+ other apps and the phone is 99% lag free. Use Facebook, Instagram, Twitter etc on phone browser and the 1GB Ram phone will work good without lags.
These 'social and IM apps' are always running forcefully (even in background) and cannot be kicked out of ram by Android when it gets low on ram, whereas most other apps (including bloatware) are kicked out of ram immediately the moment Android is low on ram and it needs more free ram.
Ram full = lag
Battery and Ram boosters = junk
They are the culprits of lagging in 1GB ram phone, because they forcefully stay in ram all the time, even when the ram is full!
If people still want to use many 'social and IM apps' on 1GB ram phones, use greenify and greenify them.
Bloating 1GB ram device with Line, Viber, kakaotalk, tango, whatsapp, oovoo, wechat, imo, kik, Facebook, snapchat, messenger, Skype, Instagram, BBM, twitter, LinkedIn, ching pong, ping ping, etc all at the same time gets your 1GB ram on crutches!. Use only what's REALLY necessary.