vvv Seriously, all Perfume's albums are as great as the others, on their own concept; also they're very solid. Personally I recommend GAME, JPN and COSMIC EXPLORER, on that order, because they're very distinctive amongst the others and it shows their evolution on music.
vv it depends on what sort of sound you enjoy. if you're looking for a specifically electronic sound then GAME or Triangle are good to start, but looking at your charts and such you might enjoy JPN as a starting point.
The only song I like from COSMIC EXPLORER is Miracle Worker, because I felt it had some of the old Perfume, with its plaintive, worrying vocals, combined with it's glittery EDM synths. It's like GLITTER's older sister that is wearing sexier clothing and going to music festivals now. I'm a little disappointed that the rest of the album wasn't like JPN's older sister haha.
I probably spoiled JPN for myself by listening to all the singles as they came out. By the time I listened to JPN it just felt like a disjointed greatest hits album. A lot of tracks are great but I feel like it doesn't come together as an "album" as well as the others.
Perfume was a great group to listen to during my high school years and younger 20's. Their music got me through pretty harsh times and made me feel awesome. Unfortunately, their newest albums just don't have the same spirit like their first 3 albums. :/ Time to move on.