As I understand it, the main appeal of choosing heatseekers over ImRecs in WC3 was because the former had moderately better speed, turning rate, and explosive yield (about 450 vs 350 IIRC). However, with anything lighter than a Longbow or Lance falling to a single ImRec, the advantage disappears, so the ImRec's lower spoof rate and ability to be launched from any approach angle makes it the preferred choice.
On another note, has anybody here tried to play WCIV "Price of Entertainment" style? In other words, use Leech weapons whenever possible. If flying a craft with no Leech guns, you carry as many Leech missiles as possible and do not use any other weapons on a leechable enemy until the Leech missiles are expended. If flying a craft with Leech guns, then leechable enemies must be leeched.
On another note, has anybody here tried to play WCIV "Price of Entertainment" style? In other words, use Leech weapons whenever possible. If flying a craft with no Leech guns, you carry as many Leech missiles as possible and do not use any other weapons on a leechable enemy until the Leech missiles are expended. If flying a craft with Leech guns, then leechable enemies must be leeched.