Which is the best manga?

kind of funny,,because manga in my country means water wose!! LOL!!!!!

Naruto is a good series. Most people over look it these days because it's "Mainstream" though. Peacemaker Kurogane is also good, even though they've only started reprinting the series (the anime is completely released though). Saiyuki is a good series. So is Death Note, Trigun, and Lupin III. I could recommend several more, but it's girly or soppy stuff like Fruits Basket and I am not quite sure that you are into that.

Well, it depends on your interests. Personally, I wouldn't recommend Naruto unless you've read very few shonen mangas before. Naruto really doesn't stand out much from its shonen manga counterparts and it will get boring if you've already experienced something similar. If you've never read shonen though, go for it.

I'd recommend the following:

Monster by Naoki Urasawa
20th Century Boys, also by Urasawa
Hunter x Hunter (it looks like your typical shonen, but it's actually unique, especially in terms of its energy system and its villains)
Level E (extremely weird twists, very short as well)
Gantz
Berserk
Death Note (nice plot twists)
Neon Genesis Evangelion (actually, I'm not sure if the manga's any good. You might want to check out the anime for that one)
Team Medical Dragon (got some interesting insights into the Japanese medical system)

Good luck.;]

Berserk for sure. Unless you're not really into badassery and violence and blood and monster things being you know killed every other page. Or if little glowy naked fairies disturb you.
I like Shugo Chara, uh... welcome to the N.H.K if you can handle some "mature themes" every once in a awhile and a story chock full of otaku humour. Maybe not the best thing for you if you're only into stuff that gets dubbed because it'll reference a lot of stuff that never made it over here.
The Third is also a good manga, if you like a main character who's female and has a sword... and a talking tank.
Ai-Ren's a real nice romance/drama thing but afaik there's no official english version so you'd have to find it on the internets...
Hidamari Sketch is hilarious
Doujin WOrk is also lacking an official english version but it's great, again would be geared at an older audience.

Might not help you any but hey, I've only heard of two of the things on your list and only actually read one of them. (Detective Conan and Hikaru no Go, HnG being the one I've read some of)

"Reborn" is a good one. "Dance in the Vampire Bund" is HOTTT. I know u can read Reborn online, but i'm not quite sure about Dance in the Vampire Bund.