Hi Mukesh,
Thicker the cables, costlier they are. Shorter the run, thinner cables are sufficient. For your LCR channels, 16 Gauge should be more than sufficient. While 30ft ones need 14 gauge.
Calculate the total run of LCR and total run of surrounds and atmos. If your budget allows go for higher end cable like belden (tinned copper ones) for LCR and any local brands for the longer run lengths.
Alternatively, you can go for 14 AWG for all the speakers as well. All depends on how deep your pockets are.
You can visit cable crafts in SP road. They are authorised distributors of many brands. I bought Belden cables from them about 6 years back. They also have good OFC cables from local brands as well.
There are other cable shops in SP road which sell speaker cables as well.