Most of them are unknown for me, but I'm glad to see a Tegami Bachi fan finally, sometimes I'd like that series get the popularity that deserves. Beautiful story. =/
However, I am not following it currently because of the scans, so I want to buy it soon, as well as Owari no Seraph when it comes.
I'd ask why Reborn as favorite, but I won't discuss it. I dislike Reborn, but I don't discuss with who likes.
Tsunayoshi Sawada is a really fun and good lead and one I could relate too all the way through. His own dilemma with the larger than life issues he confronted, along with Akira Amano's excellent storytelling skills of a good knack for having amazing comedy sprinkled throughout even super serious times made it a blast. One of the funnest stories and so many excellent character designs all around. Probably in the minority but I really liked the Kokuya Gang arc and Future Arc/Choice as my favorites. I wish it never ended.
Don't get mad with what you are going to say below. XD
In my opinion, Tsuna was a boring person who didn't see what was around him and constantly denied your condition as leader of the mafia, without his power he was a commoner with no courage at all. I have favorites characters in Reborn, of course, there is many good characters, but Tusna is far of them. I'm not sure about storytelling skills because Reborn ended in the same way as began, nothing happened to change Tsuna and others characters, the entire story was useless with this ending in my opinion. Reborn had the worst final that I could think, probably this is the worst final that I saw in my life. Because of these motives I deslike Reborn.