I was new to LEDs a while back and understand your confusion. It can be somewhat daunting to know what to buy. There is a lot to know when going with LEDs.
After doing some research and some experimenting I use the following on my solid state pins:
Clear dome 2SMDs for inserts, color matched except for the yellow and orange inserts where I use cool white. Cool white 2SMD LEDs for clear inserts. I always buy one or two extra of each color because I inevitably count wrong and miss an insert. Be thorough and careful when counting each color that you will need for the inserts and you won't need to order extras.
Frosted dome 2SMD LEDS for the GI. Cool white LEDs have a hint of blue in them. Warm white and sunlight LEDs have the more traditional look of incandescents and are more toward the yellow side of the color spectrum.
Since you are just starting out, I would keep it simple and go with cool white for the GI if you want bright or sunlight for the GI if you want a more yellow, traditional look. If you are an experimenter, like I am, then buy a few color coordinated LEDs to match the playfield and see if you like them. It's a matter of personal preference though. You might want to look up some pictures of playfields with different colors of LEDS to get some idea what you like best, but seeing LEDs in person is very different than seeing them in pictures. LEDs 'pop' when you see them and the camera doesn't pick this up well.
I experimented with some color GI and sunlight LEDs with Mr. & Mrs. Pac-Man and like how it turned out, but you don't want to go crazy with the colored LEDs above the playfield (general illumination or GI)!! I went with cool whites on Harlem Globetrotters and I like that look too. Very bright!
I like Comet LEDs. Their cool white LEDs are really bright and do a good job of lighting up the playfield and really 'pop' when used under clear inserts.
Check this out:
There used to be some cheaper 39 cent LEDs on the market, non SMD. Avoid these; they are junk. Just stick with Comet and you will be fine.