Hmm... Let's see... That IS a toughy!
I like MONSTER myself, but that's just me.
It'll grow on you... But anyway! Here are some of my recommendations (minus MONSTER and ACTION)!
1. LOOSE
2. GREEN
3. IN THE LIFE
4. C'mon
5. MAGIC (If you like ayu-ish songs, PRAY and Ichibu to Zenbu are the songs you would probably enjoy! <3)
6. Brotherhood
7. SURVIVE
8. ELEVEN
9. FRIENDS/FRIENDS II
10. B'z The Best ULTRA PLEASURE/ULTRA TREASURE (If you're new to them, this is actually where you want to start at! ULTRA PLEASURE has most of their hit singles, in exception of BAD COMMUNICATION and 人生の快樂. Meanwhile, ULTRA TREASURE has their most loved album songs and singles. Disc 2, at least the first track, was voted by fans!
)