Ikebukuro vs Shinagawa

Hey, I am going to spend the summer in Tokyo for vacation. I found two places that fit my budget, one is in Ikebukuro and the other is in Shinagawa.

The Ikebukuro place is about 5 minutes from the JR Yamanote Line in Ikebukuro.

The Shinagawa place is next to Aomono-Yokochō Station. It is not really THAT close to Shinagawa Station.

I've never been to Japan so I'm kind of a tourist! It seems like Ikebukuro is more in the thick of things which I like because I like walking places, while Shinagawa seems kind of distant. However, I've heard Ikebukuro can be a little sketchy and I like that Shinagawa is semi-close to Odaiba.

Any thoughts, suggestions, and recommendations would be welcome! I'm all ears! :)

The only real advantage Shinagawa has is that it's a shinkansen rail station. If you're going to do trips outside of Tokyo, either west or north, then Shinagawa could be beneficial, though you say you're not going to actually be near Shinagawa Station. And being 'closer' to Odaiba is really true, transport-wise.

Ikebukuro has a direct link to Odaiba, though from the 'rear'. The area is probably more lively, well, definitely more lively than Shinagawa and you'll fin anything you need there. Ikebukuro station is massive, serviced by enough lines to get you to where you need to go. About it being seedy, as long as you avoid the possible areas (don't know which), you should be alright.

In my opinion Ikebukuro is 'seedy' in a very much 'seedy for Japan' sense. Sensibilities might differ, but if you're at all familiar with any Western big city, you've probably come across much worse.

Especially if it's your first time in Japan, being more central with good access to various other main Tokyo areas would be more important than access to Odaiba, so I'd recommend Ikebukuro.

I would definitely choose Ikebukuro. The JR Yamanote line loops around the center of Tokyo so you can get anyplace easily.
Seedy? I went through that station every day for many years and even then it was far from seedy. Not as upper class as shibuya or Shinjuku, but not as "seedy" as Ueno. The huge Tobu dept. store is about the best in Tokyo. Restaurants on floors 10 through 13 at least. And Seibu is a good dept. store, too. They both have large "grocery" stores/ prepared foods in the basement so you can buy dinner to take back to your room. Try Gobo Salada. Very unique and delicious. And their bakeries are marvelous.

By "rear", John B may be referring to the Yurakucho subway that takes you to the less busy end of the Yurikamome line, a computer-controlled train that goes around Odaiba.
At Ikebukuro, get on the front car of the Yurakucho subway train. It takes about 25 minutes to TOYOSU station. Go upstairs and out exits 6B or 7 that are near the Yurikamome station. You have a good chance of getting the front seat where a driver normally sits (there is no driver).