DQ 1-4 were some of my favorite games as a kid. I really enjoyed the class system in 3 and really liked almost everything about 4. I've played most of the non-mobile remakes of these games that came to the US and enjoyed replaying them.
DQ 5 and 6 I never got around to playing. I own the remakes on the DS and probably will get around to them someday. I did play about the first 5 hours of DQ 5 with a translation patch on an emulator many years ago and enjoyed it.
DQ 7 came at a bad time for me when I wasn't playing many console games because I was too into online PC games. I own it, but never got around to playing it.
DQ 8 actually was a game that started to get me back into console gaming and console RPGs. I remember at the time it had been a long time since I had played a console game since I was so into MMOs like Everquest, Dark Age of Camelot, and World of Warcraft at the time. I played ~150 hours of it and loved it. I especially liked the skill system.
DQ 9 was amazing. It expanded on DQ 8's skill system and added a ton of stuff to do in post game with random dungeons. I enjoy grinding/progressing my characters and the game rewards that with lots of classes to grind up. My save has 250+ hours on it.
Unfortunately, even in the extremely unlikely event that DQ 10 comes to the US, I probably won't play it since I have enough online games available to me that I can't add another one. I'm just hoping that DQ 11 won't be a mobile game whenever they do decide to release it.
As far as bests, it's really hard to say since the games were important to me at different times and have to be judged against games of their time. I spent tons of time on 3 and 4 as a kid because there were only a few really long, good RPGs on consoles in those days. 8 and 9 were games I played even though I wasn't doing much console gaming at the time and both really showed me that JRPGs still can be great games if done right.