For new players, I think right clicking heroes are best to begin with. Sniper, Viper, Razor, Wraith King, Bristleback are easy right clickers. In my opinion. Also Sniper and viper are very versatile and some changes in their build can counter any line-up. Also I find Abaddon to also be very versatile, you can go for semi-support or carry or even make it into a core. But Abaddon might be bit overwhelming. Wraith King is better alternative (compared to Abaddon) for new players with passive crit and lifesteal, a stun and free aegis ultimate
P). You can try right clickers to learn about game basics and later try heroes like Jakiro, Lich, Venomancer, Death Prophet, Troll Warlord, Tidehunter, Sven.
Then depends on what role you like pick supports like CM, Earthshaker, WD, Shaman, Pugna or carries like PA, Drow, Luna, AM, Gyrocopter.
Finally, you can try the tough ones like Invoker, Visage, Chen, Meepo, LoneDruid.
Keep your hero pool to 10-12 heroes which you can play well and that is enough. Eventually you'll have 30-50 heroes in your pool.
But try all heroes at least once at least in bot match.