Chanting Lord Names is always great and connect directly to lord. Mantras are good if you have any specification aim in mind, most of the time either for some specific sadhnas, might be some tantra sadhna or any ritual requirement.
Difference between both I feel, Chanting lord name is like landline connection, always keep you connected with lord, as you might keep on remembering him every time, at each meals, starting any task, finishing any job, bathing, cooking, even drinking water. Mantra chanting is just like Mobile set, you have to charge again and again.
But, the best one is use combination of both, like chanting your favorite mantra in the morning like Gaytri Mantra or Hanuman Chalisa and keep on chanting Lord’s name when ever can and as maximum as possible.
Also reading Upanishads / Scriptures like Sai Satcharitra, Gita, Ramayan has own importance. It make us feels presence of God near us.
But above all this, If God really need something It is pure love and devotion towards Lord and nothing else. Merely chanting Mantras and just chanting Lord Name one can attain worldly pleasures even a blissful life, but not God. So, Keep on chanting Lord name but with upmost devotion and Love!
om sri sai ram!