which one is most popular DCS?

Honeywell

Honeywell has better performance.

I just need first to identify the real DCS players in the market which are:

1- Honeywell (Experion PKS)

2- YOKOGAWA (Centum VP)

3- INVENSYS (I/A)

4- EMERSON (Delta-V)

For ABB, if we are speaking about800xA, then this is not a DCS; this is just a toy compared to the above4. ABB bought ELSAG BAILEY and destroyed it. ELSAG BAILEY had true DCS Systems like infi-90 and Freelance (the best DCS I have ever seen in my life). Freelance belonged to Hartmann & Braun which was the king in the field of Automation and Instrumentation.

And yes, YOKOGAWA is the cheapest but Honeywell and INVENSYS are the best.