which ghastly is better for pvp?

1st

 

2nd

 

thanks

Gastly needs 31 speed for pvp with a timid nature.

sp.attack is not important?

sp. attack is important. just not as important as speed here. gengar already hits like a ton of bricks, your priority should be making sure you attack first on account of being so squishy.

First

28 speed with timid nature is not enough?

the 2nd has 29 and hasty nature, that boosts speed too,

The reason why everyone wants a 31 speed Gengar is the mirror matchup and the rarity. Its a very common Poke so most ppl have a 31 speed Gengars and you will lose every mirror matchup with one of yours.

You can train your Gastlys and use them for pvp they will work but you will have a disadvantage which you could easily dodge by searching a 31 speed one.