Different forms of God are conceived in Hinduism to meet the different tastes and temperaments of people. While God as Brahman/ Parabrahman is one and is amenable for worship in different forms, saints and sages always advise seekers to concentrate and worship one God whose form is ishta – the most dear to the heart. That way focus will be far better instead of fritting away energy in different directions.
Here is a story narrated by Satguru Mata Amritanandamayi (Amma) which is quite apt to answer your question:
Dig deep at one place
Once there was a famous devotee. A man from the next village heard about him and therefore came to see him. The visitor waited outside the front yard of the house as the devotee was performing his worship inside the house at that time.
The man peeped inside and noticed that the devotee was sitting in front of his pooja shrine and doing the worship of Lord Ganesha. The visitor, seeing this dug a hole in the ground. The devotee then started worshiping his Guru. The visitor, now dug a second hole. After finishing the hymns praising the Guru, the devotee then started worshiping Lord Muruga. The visitor dug a third hole.
As the devotee then proceeded to worship Lord Vishnu, Goddess Lakshmi, Lord Shiva, Goddess Kali and so on, the visitor too dug one hole each corresponding the the God worshiped.
After finishing the puja, the devotee came out and he was surprised to see so many holes at his yard. He shouted at the visitor: “What is this? Why have you dug so many holes in my yard?”
The visitor said, “I wanted to get some water and so I dug one hole. Since I didn’t get water there, I dug the next one and the next and so on. I have dug everywhere but could not get any water. Had I dug at one place deep enough, I would have got the water by now and need not have wasted my time”.
The devotee understood immediately. Had he surrendered to any one of the Gods wholeheartedly and concentrated worshiping him, he could have become a liberated soul by then.
[Amma: The Gods and Goddesses have diverse forms, but in reality all are one. The various names and forms are only to help us in our spiritual practice to suit our diverse tastes. Each one can choose a deity according to his taste and mental make up which will serve as the ladder to reach the supreme.]