@patelkunal89 

Hey

This is not an uncommon question, the two are quite close in offering

The Deco is designed to be a wireless mesh system that connects either directly to your ISP Router, or straight to internet (FTTP).   Its primarily for easy of use as a one stop mesh system and are generally sold in 2 or 3 node units.   Totally controlled by an App, designed for very much home use and have quite commonly used features, but not fully featured.

The Archer range is a different beast, they are primarily replacement routers to use instead of your ISP router.    The are configured as a SOHO router and tend to be more fully featured compared to deco, few more features and web GUI driven, but harder to setup overall.    These can be extended to MESH using the OneMesh plugs, but that is an optional feature, its primary goal is single router.   They are more powerful and slightly better performing vs deco. 

OK so summary..

Archer.... For apartments, small houses or people who require more advanced tweaking.  Slightly Gamer or Power user based, someone who Mesh isnt really needed, but might want add it later

Deco...  Mesh for larger houses, less featured but app driven and easy to setup.   More you 'home' grade stuff.   For people who just want WiFi everywhere now..  easy to setup, no real configuration needed and visually pleasing.

If you are running cables, then either will work tbh.    Personally Deco is the more common used and the performance of the X20 or higher is very good!