Which one is the best option for RF Ckt simulation and layout- ADS or SpectreRF?

Depends..
If you work with VLSI, Cadence ADE is better..
If you work with MMIC, ADS is better...
However..
-Your model should be supported by simulation environment
-Process file should be defined first..
-Complex layouts are more difficult with ADS..
-Cadence ADE is more flexible in terms of exporting,verification,cross probing etc.
-In term of simulator, sometimes ADS is more robust, sometimes Spectre-RF, depends on circuit complexity and model accuracy.

So, as you see it has many parameter that impact which tool is better for your application.