Level 4 Warlock decision (5e)

Hey everyone!

I have a question to pose to the community. I am playing in a 5e campaign as a warlock Fiend blade pact. The party just hit level 4 and I have access to my first ASI or feat. Here are my current stats: STR 14 DEX 13 CON 16 INT 10 WIS 9 CHA 18

So I have considered my options and I either wish to bump my CHA to 20 or take the Warcaster feat. I am having a hard time deciding and was wondering what you all thought. I find this community to be a great resource for information and could use any and all advice.

Thanks!