Every hero has their pros and cons, so there isn't any best hero. But here are a few heroes that you can try.
Slardar (str): Has amplify damage which reduces enemy armour by 15, easy kill Axe (str): A tank that can deal alot of damage and instant kill using culling blade Terrorblade (agi): Carry hero, very VERY weak early game, powerful end game Zeus (int): A very powerful nuker and an ultimate that can damage all heroes Slithice (agi): Pure ownage, can kill almost any hero 1 vs 1 Batrider (int): Able to do lots of damage and chase thanks to sticky napalm Luna Moonfang (agi): Can bounce attack up to 5 times and a very scary ultimate
In the end, you should try heroes for yourself. You can always go single player and choose an AI map. Then you just need to type in the command -ar. You get a random hero, try it, see if you like it or not.