It's always going to be a toss-up between High Elves and Lizardmen.
Lizardmen bet all their marbles on a big ugly from who has Loremaster and adds an extra die to every cast. No doubt about it, that's some heay magical firepower.
High Elves Will generally bring a Banner granting +d3 Power dice/turn and an Arcane Item which takes an enemy Power Die and turns it into a Dispel Die, they also have a 10 point item to grant an additional spell.
Both Lizzies and Helfs have access to all eight Lores from the core book, but High Elves also have their own Lore. High Magic isn't that great, but its spells are super-cheap in eighth edition, so you'll cast more per turn.
Unlike Lizards, high Elf Hero casters also have access to their full nine Lores. Lizard hero casters get Heavens only.
Lizards have solid anti-misscast protection, High Elves have only limited protection if they burn an Arcane slot for it.
Lizards can have Loremaster, High Elves can take an item which lets you chose spells instead of rolling.
Both are very strong in the magic phase, but in different ways. Lizards have the edge in raw power, High Elves in finesse.
Unless you count Teclis. When the big T is on the table all bets are off. Loremaster, any Lore, immune to one miscast/phase, every double of any kind is irresistable without miscast ad he can permanantly remove an enemy spell from play.
Looking for a friendly wargaming club on the Isle of Wight? Drop me a line.
Sisters of Battle - The Order of Glory Undimmed - 2'500 Points | High Elves - House Cyredeth - 2'500 Points | Bretonnians - The Muster of Sir Jules Estelle - 3'000 Points