Disneyland/universal studios booking

I am going to Disneyland and universal studios from April 7-10 or April 15-16. Do you think it is better to book in advance or on the day? Would you just book from the official site or from discount sites like mousesavers or arestravel.

https://www.mousesavers.com/california-discounts-deals/universal-studios-hollywood-discounts-and-deals/#ares

aRes Travel | Cheap Hotels, Vacation Packages, Discount Attraction Tickets to Disneyland, Legoland

How reliable are these sites? I’m from abroad visiting mainstream US for the first time so just want to make sure.

Re: Disneyland/universal studios booking

Book in advance definitely! You don’t want to be in line for tickets the day of and by booking in advance you can have your Fastpass selections made soon enough.

For the record, MouseSavers is reputable.

I’d recommend purchasing them from Undercover Tourist (which is where I believe I purchased mine in the past). https://www.undercovertourist.com/orlando/?pid=w3bl1nksp3c14l (There’s a link to this on the MouseSavers site)

Re: Disneyland/universal studios booking

Yes Shaas try to find a deal. I'm sure there'll be plenty of sources for that i'll try to find it for you