Comet Pinball LEDs are the best deal out there. And the product and service is top notch!
From my experience here is what I have come up with regarding some basic ground rules in LED choice and use:
1. I prefer the frosted 1SMD 5050 for almost everything as it gives a nice bright smooth dispersed light for inserts, under plastics for GI, and behind the back glass. Only exception is using Retros when you want that pinpoint of light showing as with an incandescent.
2. For back glass and under playfield plastics use warm white LEDs behind warm colors such as yellow, orange, and red, and use cool/natural white behind cool colors such as blue, green, and purple. You can use a colored LED for a "special effect" in some areas if desired. Again the frosted 1SMD 5050 works great here.
3. For inserts you can also use the frosted 1SMD 5050 but match the color of the LED to the color of the insert. The only exception is for yellow inserts. Do not use a yellow LED under a yellow insert. Instead use a warm white LED. Yellow LEDs are not bright enough and are only useful behind white inserts.
4. Use different color LEDs under white inserts to give you a more colorful playfield if that is the effect you want.
5. Use colored LEDs under playfield plastics to create a more modern colorful look if that is the effect you want.
6. Use specialty LEDs such as color changers and flex heads for those areas that may need them. Flex heads are good for where you have a sideways mounted bulb under an insert but I have found that the regular frosted 1SMD 5050 LEDs do put out enough sideways light to work just fine also.
7. Another very useful specialty bulb is the older style "Bullet" LED with a frosted lens. These are great to use if you have a bulb that "peaks" out from under a plastic and shines right in your eyes. This style of LED shines very little light to the sides so it reduces the brightness that hits your eyes. Just use a frosted warm or cool/natural to match the other LEDs in that area.
8. Every game is different so feel free to experiment with different color and type combinations. It is always a good idea to purchase a few extras so that you can experiment.
9. The most important rule sometimes is to not follow any rules. If you think it might work give it a try. If you think it won't work give it a try anyways! You will never know what works until you try. It's only a bulb and it can easily be changed out if it doesn't work for you.
So my suggestion to get started is to get a bulk pack of both the warm and cool/natural in the frosted lens style found here:
The bulk pack pricing of 59 cents is great! These LEDs can be used everywhere and will be a good start. Just remember to use the warm white behind warm colors and the cool/natural white behind cool colors. You then can also pick up various colored LEDs to match your inserts and for any "special effects" you may want to experiment with.
Just remember it's your pin and what looks good to you is what is most important!!