Soraka is one of the best supports in hole game.Her heiling spells are really good So if you ask me : better is support Soraka (my opinion )
I played with soraka on top once versus jax and i owned him and i think that soraka is good for mid,supp and top trust me....i had 6/0 in 15 min versus him but u need to practise with her so u can silence him when u need
Hmmm i guess support is better couse she doesnt fit in currter mid lane or top meta but u could play it for fun on mid or top i guess shes pretty decent on top couse of her E poke which has no mana cost if casted on enemys i played few soraka top games and i actualy did pretty well with her about 5 or 6 games none loses, but she kinda falls of late game couse of no burst even if u play her on mid or top in later parts of the game u will still have to act as support with her. For top or mid i would go Tear/Grail, Rlyas Rylai's Crystal Scepter, Spirit Visage, Merc/Cdr boots and Raba/Zhonyas