I want full rounded and chubby cheeks like Selena Gomez, which fillers will help or should I do fat transplant? (Photos)

It seems like you are seeking global uniform volumization of the cheeks, rather than focal filling to create contours and angles.  Your face appears lean, but Selena's is more full.  You may want to consider Sculptra to stimulate collagen growth rather than the injection of multiple syringes of filler.  Fat grafting may be another option.  Consider a consultation with a plastic surgeon experienced with facial enhancement.  Good luck. 

Facial sculpting and contouring can be created with well-placed fillers (Voluma, Countour, Radiesse, Bellafill) and Sculptra, which would give improvement in facial balance. Fat or implants are alternatives. I recommend getting a formal evaluation with a facial sculpting expert. Best, Dr. Emer

Hello bellblueyCheek implants are available in a range of different shapes and sizes, they are mostly customized to fit a specific facial structure. Fillers such as Juvederm Voluma, Radiesse and RestylaneLyft are great alternatives to cheek implants, also fat transfer or injection can be done.

Both implants and fillers in the cheeks can create good results for patients.  Both can build up the cheeks and create contour.  You must balance the pros and cons of each procedure and do what you feel is the best decision for you.
Fillers:
Pros: No downtime Reversible Quick
Cons: Temporary More expensive in long run
Implants Pros: Permanent Great for patients with poor bone structure Less expensive overtime
Negative: Risks associated with surgery Possible infection Downtime
I hope this helps!