What is better for new player like me!!! 
Frager vs Thunder
Fragger. Only advantage Thunder has is +10 life. Fragger is better in every other aspect. Also blinding yourself with conc nades will seriously pss off newbies.
For new players, Fragger, he can be very effective, have a good amount of HP, and since he’s slow, it’s easier to aim with him.
Thunder is slower, but his weapons are more difficult to use (since his LMG deals less damage, and the AK have a bigger recoil than the M4A1, the Stark is an exception), also, it’s pretty difficult to rush to the enemies after stun them, since Thunder is even slower.
However… Thunder can be more of a Team player, he can make the enemies vulnerable for his team mates, as well temporarily disable enemy defences with his EMP, allowing for your team to rush the enemies and take them out easily.
tl;dr: Fragger for newbies, Thunder for Experienced players.
Fragger is better for new players, especially those who still have bad aim. If you have bad aim, take a loadout with the K-121 (his default weapon) since it gives a spray and pray feel.