Oblivion: Next had more filler, people dont like TRY because its the first of the Slayers series with a season long arc. I happen to like TRY even if Filia took too long to come to grips with shit.
I think the first series was probably the most charming, with Next having the best Filler, and Try had the best ACTUAL story, but also had some amusing eps and better art.
The OVAs arent bad but the nod to fan service gets on my nerves. Still it seems like half the OVA eps take jabs at fanservice by making characters like Naga seem so absurd and playing off the contrast between Lina and herself. Jeffry's Knighthood was probably the best OVA.