Congratulations on deciding to marry. Wonderful to know two prospects have been identified.
Before you try and convince your parents on your choice, you need to be sure why you are rejecting their choice. What about his lifestyle, goals and principals in life that you find unsuitable? Does he have a flashy lifestyle? Is he into partying? Does he give importance to money (he is into making more money?), brands, high flying lifestyle, etc?
When you reject some profile, you need to have valid reasons. To convince your parents. Likewise why do you feel the prospect you selected is the best for you? Is he closer to your age, is his job profile more appealing, does he come from large/small family, is he better looking, does he talk about helping people/animals/nature, etc?
You can write down the advantages and disadvantages of marrying your choice and another list for marrying your parents’ choice. Compare the lists and see; this may give you some clarity.
Once you work these out, you can discuss with your parents. However, you will need to listen to them with an open mind, when they feel their choice is better. Give them an opportunity to list out their reasons. Think about these points, before you compare with your choice.
Hope this helps you arrive at an answer. Do take some time to work this out. Remember, marriage is for keeps!
All the very best!