Doesn't damage battleship shields, takes a long time to start tracking, can be intercepted en-route, takes longer to reach the target, can easily kill team mates, has a minimum launching range...oh, and only has 70 shots vs the SN's infinite shots...
Nova > SNAC in terms of firepower and power efficiency
SNAC > Nova in terms of price, ammo, ease of aim, chance to hit, less friendly fire, no interception, no suicide shots.
Thats my experience. Nova's have killed me more than I've hit anything else... so my accuracy ratio with it must be -80% or something.