The three official onsite hotels are:
Loews Royal Pacific Resort-
http://www.loewshotels.com/specials/Royal-Pacific-Resort
Hard Rock Hotel-
http://www.hardrockhotelorlando.com/
Loews Portofino Bay-
http://www.loewshotels.com/Portofino-Bay-Hotel
PB is typically the most expensive and RPR the least (though it is still a breathtaking beautiful luxury resort). None of the resorts are inexpensive exactly, but I feel they are well worth the money. Take a look at all three and see which best fits your taste and budget.
All three are within walking distance of Citiwalk and both parks. All three give you early entry to Wizarding World as well as unlimited Express Pass (vs. if you stay offsite and purchase Express Pass separately which only allows you express entry to each of the qualifying rides 1x per day. Onsite EP lets you in as many times as you want all day each day of your stay including the day you check out.) There are only 3 (maybe 4?) rides that don't accept EP-- Harry Potter's Forbidden Journey, Pteranadon Flyers (which you must have kid BELOW a certain height with you in order to ride), and Rip Ride Rocket at Universal Studios. (I'm not sure about the new Minion Mayhem at US. But I'm sure someone else here can tell you that.)
You typically get the best deal on the onsite resorts by booking directly through each hotel's website, rather than purchasing a package deal through Universal. If you have
AAA, they typically offer discounts for that, PLUS you can get 10% off at most of the eating places & gift shops within the parks by showing your AAA card. There are also the Stay More Save More (SMSM) rates at the hotels which give you cheaper rates per day the longer you stay.
Offsite "partner" hotels do exist, and can be found through Universal's website. I have never stayed at one, but my understanding is while they do offer some perks like early entry, they do not give you Unlimited Express Pass. If you go during an off season you may not need Unlimited EP and you may find the "partner" prices more to your liking, but I personally cannot image staying anywhere but onsite. June is NOT off season, so EP, to me, would be priceless.