I would like to install auto gate system on my existing gate. Any reputable brands I can go for? Price is not an issue, most important is quality.

This will depends on what type of gate are you having. Sliding, swing or folding. It will also depends on how heavy are your gates. For the heavier ones, better to get the heavy duty ones to avoid problems later on.
There are many brands in the market like Jackpro, Magnet, DC Moto, OAE, Hermes, FAAC, DEA, Jackpro, Radion, Vigitronx, Telcoma, Celmer, Comex, etc.
Prices can range from 1k to 3.5k Also depends on your gate type.
Most important is to get a reputable supplier/ installer that will be around for after sales service.