Its been so long since I played Symphonia so I can't make that accurate of a comparison and nostalgia makes me want to say Symphonia is better than it actually was but I know Vesperia was better in design, story, and characters. It also helps Vesperia that it's so recent in memory after putting 100+ hours into it. Though if I do remember correctly Symphonia had a story involving 2 different parallel worlds or something and I thought that was pretty damn cool.
You know, while looking up strategy guides for Vesperia I did see this blonde character/avatar every once in a while but didn't look into it for fears of being spoilered. I just thought the character would join my party later in the game and didn't want to know how. Then I completely forgot about the character until after I beat the game, lol. Well, now I have my explanation.
Personally while I think Vesperia is definitely more polished mechanics and gameplay-wise, the story is one of the worst in the series (in a series known for having lacklustre stories!)
The characters are nice though! But overall I prefer Symphonia and feel more attached to those characters