Which group should i choose popular, or middle? & a girl invited every1 to her party cept me!?

i have a group of friends that are in the middle-you know, like not popular or wierd.then i have another group of friends recently and they are the popular ones. my middle friends get sometimes mad at me when i sit at lunch with them and i do switch off tho! idk what to do, or who to choose. my middle friends and i had 2 HUGE fights about this. also, i have another question lol. theres this girl lexi, and she invited every1 to her bar-mitsfa exept 4 me and 3 other girls. i sit with her at lunch too, and she invited GUYS before me that she dosnt even talk 2. what should i do?