The retro series from CT looks really nice in EMs, just make sure you get the "warm" style white. They look nice in GI lighting, but can be kind of pricey. Considering the relatively low number of bulbs in the GI, it is worth the small investment to keep your plastics from warping due to heat.
I use warm frosted in my backglass, and the frosted ones diffuse the light well for that application, and can be had at PBL for really cheap. I still keep regular bulbs in my backbox for match, tilt, game over and number of balls because they spend a lot of time off and would require non-ghosting premium bulbs.
Under the PF, you will need to use non-ghosting LEDs and will really need to look and inventory almost every connector due to the fact some bulbs are mounted sideways and some are head on. This is the expensive part of the LED conversion, and seldom is worth the cost.
Personally, I just try to find the best mix of benefit to cost ratio for my EMs. My main concern is preservation of the backglass and plastics as best I can for as little investment possible. Under playfield and inserts is too tricky and cost prohibitive for me right now, but maybe down the road...