My favorite phrase to use when people ask me what kind of credit card to get, or whether a particular offer is a good offer, or a number of other questions is… it depends. You should have goals in mind as well as an understanding of your own situation and your own capabilities.
If you want to travel, the Delta Amex might be a bad card–or it might be a great card depending on where you live, where you want to go, when you want to go, etc. (Though given how much Delta has devalued its miles, that card will be sub-optimal for most folks these days.)
How much do you (or can you) spend every month? How much time do you want to spend managing your credit card portfolio? What kind of rewards do you want–cash or miles/points? If you want to redeem your points for travel rewards, then where do you want to travel? And so forth.
Applying for three cards at once might be a bad idea–but it might be a great idea, depending on your credit history, monthly spending capacity, required minimum spend for the card offers, and the bonuses offered on the cards. When you’re first starting out with this stuff, you won’t necessarily have a good idea about how to resolve the “it depends” issues, but you’ll eventually get the hang of it.
I advise that if you want to use credit cards for travel, sign up for cards with a specific trip in mind (“I’m going to Disneyworld!”) or at least some sort of travel goal (“I’d like to fly first-class to Europe”). This will provide you guidance on the type of card to sign up for. Hotel and airline loyalty points/miles tend to be devalued every couple of years, so your points and miles are depreciating assets. Use them or lose them!
That said, I can give you one simple rule to get started. Everybody should have a no-annual-fee 2% cashback credit card as their default. You should be getting at least 2% back on all your spending. For a long time the Fidelity Amex was the best card of this type, and I still do recommend it, but as of right now I think the Citi Double Cash is a little bit easier.