I have recently brought a starter and the Dunwich horror delux and first Mythos pack. Should I wait to learn with the investigator decks or just use the default decks in the starter?

I'm going to assume a few things here: by "starter" you mean the core set, and by "investigator decks" you mean the recently released starter decks (Nathaniel, Harvey, etc).

If these assumptions are correct, it doesn't really matter whether you learn the game with the starter decks or the default investigator decks from the core set. Using the starter decks will probably be faster since they're pre-built with random weaknesses already chosen.

If you don't own the starter decks yet/ are waiting for them to arrive, there's no reason not to jump in with the default decks from the core set, assuming you have the time. If you don't have the core set, you'll need to get one of those, since every expansion campaign uses cards from it.

Hope that helps! Welcome to the mythos!

Yes it does by Starter I did mean core. Yes the recently released investigator decks

The new investigator decks are much more playable than the sample "default" decks built with a single core. If you can conveniently get the new ones, I would recommend them as a starting point.

But most current players did struggle through the sub-optimal decks itemized in the core rules, and we're still here to tell about it!

3 hours ago, Carthoris said:

But most current players did struggle through the sub-optimal decks itemized in the core rules, and we're still here to tell about it!

This player survived.......my investigators though, alas, did not.

On 8/31/2020 at 10:27 AM, Carthoris said:

But most current players did struggle through the sub-optimal decks itemized in the core rules, and we're still here to tell about it!

I remember those days! O the horror (and the trauma)!

Carthoris is right. Only having the Core set at the beginning and the suggested decks were, well, an experience. You are lucky though, because if you have Dunwich too, you have a lot of great cards. Deck building is a lot of fun and if you have a background in other deck building games, you may prefer that option.
That being said, this is a time consuming and addictive game, so if you have the pre-built investigators and want to just jump in and learn the game and then branch out to deck building, that works too.
And as usual, I gave no actual advice, just laid out options, so was probably not very helpful!

I think the main goal of using the "crappy" pre-build decks of the core set is that you should be able to realize (after a few plays) which cards are really useful to your investigator and which cards are just crap for them. This is a great way to learn about the importance of deckbuilding, and you can start improving those decks. If you start straight away with the new Investigator Decks (that they are indeed not "crappy") then you won't probably get as much learning from those

I feel like fantasy flight does that with a lot of the core sets for lcgs . They put in a bunch of cards that have absolutely minimal chemistry but allow the player to still learn different play styles. Kinda gets u excited for the first couple expansions so you can actually use the cards effectively.

6 hours ago, Henryillusion said:

I think the main goal of using the "crappy" pre-build decks of the core set is that you should be able to realize (after a few plays) which cards are really useful to your investigator and which cards are just crap for them. This is a great way to learn about the importance of deckbuilding, and you can start improving those decks. If you start straight away with the new Investigator Decks (that they are indeed not "crappy") then you won't probably get as much learning from those