The plan of Palpatine for Clone Army was to make it accepted by The Galactic Republic. Couldn't a Bounty Hunter's gene make it difficult? Also, what was the benefits of using Jango Fett's gene? Why didn't he pick any random guy instead of Jango Fett?
Actually, Palpatine didn't personally select Jango Fett as the template for his clone army. Instead, it was Count Dooku who selected Fett, with Palpatine approving the choice afterwards.
To select the template for their clone army, Dooku selected some of the galaxy's most dangerous men - bounty hunters, mercenaries, convicts - and pit them against each other by placing a bounty on a Dark Jedi named Vosa. In addition, Dooku had once faced Fett in combat personally (at the Battle of Galidraan), where he witnessed Fett take out several Jedi single-handedly.
Lastly, Dooku found himself impressed with not only Fett's intelligence but also his resilience and devotion to duty. The combination proved to be an ideal match for what Dooku and Palpatine had planned with the clone army, and the deal was struck.
The main reason for choosing Jango Fett's genes for this was because of his prowess in battle. Here is an excerpt from Wookieepedia:
Having captured Fett, the Bando Gora prepared to turn him into a mindless slave. It was here that Fett acquired many of his facial scars. Vosa herself came to demand of him the name of his employer, but Zam Wesell freed Fett before being injured by the insane Dark Jedi. After a long duel with Vosa, Jango Fett emerged victorious. As he prepared to finish her off, Vosa asked if he would choose to leave her dead or alive. Jango, looking at the ruined female nearing her death, lowered his weapons. Vosa murmured "He… is here." before being choked with the Force to her last breath.
To Fett's surprise, Tyranus was indeed there, and he was impressed. The bounty was a test to determine if the rumors of Fett's skills against Jedi were true. If so, his clones trained under his supervision would be very effective once Order 66, the order to eliminate all Jedi, was issued. While Fett had personally killed many Jedi on Galidraan, Tyranus considered his former apprentice a more challenging test. In addition to the bounty on Vosa, Tyranus offered Fett a tempting sum of money for an unusual task: Fett was to be a template for an army of clones. Fett agreed, and soon millions of clones were created in his likeness at the cloning facility on Kamino. Fett, however, remembered Rozatta's final wish and asked for one clone produced without genetic tampering, an apprentice and son that would become Jaster's legacy and revive the Mandalorians.
Not only was Fett supposed to provide his genetic makeup, he was to train the clones, which was his dual reason for being on Kamino.