With no luggage, you can check-in anywhere. If you are checking luggage, you must use the terminal your flight is departing from.

There isn't a difference between the check-in experience at either terminal, so I would just go to T2 to be closer to your flight. If you plan on spending time at the SilverKris Business Lounge, than T3 is certainly better (you can access the T3 lounge even if your flight departs T2).