Lilac is lovely but it creeps around the garden and is difficult to get rid of. I have a dwarf buddleia and it doesn't seem to me to have any fragrance at all but its a nice shrub and the butterflies do, indeed, love it. It seems to need a lot of water though. It very quickly droops.
Like others I have both of these shrubs, but butterflies and moths seem to come from far and wide for a drop of Buddleia nectar and I think that would be their vote.
I also have both - lilac is exquisite but it is short lived and all over by end of May. I have a large flowering white buddleia and the scent from that is very heady - I just love to bury my nose in the flowers - smells like honey to me and yes it does smell nice on a warm still night. Eaier to grow.
Only thing that would worry me (and I may be talking carp) is dwarf anything has been fiddled with and may not retain the perfume.