Hello Divyansh Ohri,
SAP CRM and SAP SD are very much related with each other. SAP CRM deals with sales, marketing and service, SAP SD stands for sales and distribution. So both work with sales (quotations and orders, SAP CRM even with presales like activities, leads and opportunities ) and both make therefore sense for you if you have done pre-sales. SAP SD is part of the SAP main system SAP ECC and elder then SAP CRM. SAP CRM is a seperate system outside SAP ECC. Some training centers say they regard SAP SD as a prerequisite for SAP CRM which partly makes sense. It is also said that the competition with other software vendors is higher in SAP CRM then in SAP SD. I am a happy technical SAP CRM consultant for more than 14 years and I think that this is a rewarding topic but this could also be said about SAP SD. So it depends on you or if you get a direct entry level job in one of these fields.
Best regards,
Thomas Wagner