LOCATION

Depends on how much $ you would like to spend really. Old Town San Diego and Hotel Circle are centrally located and have plenty of options. La Jolla, Coronado (California), Ocean Beach (California), Pacific Beach and Mission Beach areas will have more tourists attractions and photo ops while places like La Mesa, Hillcrest Neighborhood/Bankers Hill, Alpine (California), Santee all have small town charm and will definitely be cheaper than the beach areas. Good luck, hope this helps.

Are you looking for beach areas?
Mission Beach next to the roller coaster, Belmont Park is great . The board walk (Ocean Front Walk) on the ocean is a little more active than Mission Bay side across the street. The bay side is quiet. Pacific Beach next to Mission Beach is great too with a lot of shops and restaurants.

Eastlake, Point Loma, La Mesa

I use to live in Crown Point in Pacific Beach and I found it lovely. La Jolla, it's also a very nice neighborhood.

Clairemont, Linda Vista, Old Town San Diego, Point Loma, or Mission Hills are communities I'd look into based on proximity to freeways, hotels in area and especially due to attractions-beaches- cool neighborhoods- even shopping!!, and proximity Downtown & even to the Airport.

It depends what you're looking to do. If you want to stay near Downtown San Diego there is a lot to do, with more of a city vibe. If you want beachy, classic Southern California vibes, North County is great. Del Mar, Encinitas, Carlsbad (California) are all fantastic with great beaches and access to Legoland, San Diego Zoo, etc.

I personally like Coronado (California) area

JRath and other answers are great. Depends on what you want to do. If you're going to Legoland, staying nearby would be very convenient, further south Encinitas and Solana Beach are lovely all near some great beaches in SD north county. If you're interested in zoo/museums/city staying closer to Balboa Park may be appealing. Hillcrest is walking distance to these places and has some beautiful areas.

Little Italy, Del Mar, Downtown San Diego are a few places that have many things to do.

Hi Claudia. All the previous answers have great reccomendations for central San Diego. The beaches listed are the most popular and I'd like to suggest the areas of Encinitas and Leucadia to consider. They are north of the busy part of San Diego but have that quintessential small beach town vibe and maintain a lot of that history. It's a little more laid back than the craziness of Pacific and Mission Beach.
There is so much to explore along the entire San Diego coastline and interior! From ocean and beach activities to sub-alpine mountain hiking or biking, you'll never be far from any of it. Enjoy your time here!

Hi Claudia, 
Ocean Beach (California) (OB), Pacific Beach (PB), and Mission Beach are my favorites. Super close to everything. You can walk to the beach, tons of great restaurants, and things to do. Also downtown is just a 10 minutes drive. 
If looking for a more budget location, Point Loma and Mission Valley are also ok, a 5~10 minutes drive (Uber) to those beaches.