Zynga Texas Holdem Poker Room Hirarchy
First of all you need to click the "Room" button located just above the room/tables names. Only click once to stay in line with this discussion. You will see rooms in the following order which will make it easy for you to go to a particular room quickly.

100K_ like 100K_3 or 100K_6 : Minimum buy in is 2M chips

10K_ like 10K_3 or 10K_6 : Minimum buy in is 200K chips

10M_ like 10M_3 or 10M_4 : Minimum buy in is 200M chips

1M_ like 1M_3 or 1M_5 : Minimum buy in is 20M chips

200K_ like 200K_3 or 200K_4 : Minimum buy in is 4M chips

20K_ like 20K_3 or 20K_4 : Minimum buy in is 400K chips

20M_ like 20M_1 or 20M_3 : Minimum buy in is 400M chips

500K_ like 500K_3 or 500K_4 : Minimum buy in is 10M chips

5M_ like 5M_3 or 5M_4 : Minimum buy in is 100M chips

5K_ like 5K_3 or 5K_4 : Minimum buy in is 100K chips

HighRollers_ like HighRollers_3 : Minimum buy in is 10000 chips

PokerStars_ like PokerStars_5 : Minimum buy in is 4000 chips

We have omitted very small tables from this tables list as they are not required in the current context.