what is the best way to drop keys

Make GAs anyways, they will still count towards your "Gifts sent" count.

Besides GAs, another way could be to make a thread, then list the games names.

Ask people to comment to claim (number of games of your choice) , then privately message them the key on steam.
Also helps prevent bots from farming said keys.

If I recall my manga/anime tropes properly, you need to drop them while "accidentally" stumbling into a cute boy, after which you lean backwards into him and flutter your eyelashes a bit. Oh, or hold the key in your mouth as you rush to school, and drop it when you run into the cute boy while rounding a corner. If you're in some crazy music-comedy story, i guess you could just drop a piano in front of the boy (scattering the keys everywhere), and then leap to save him, tumbling you two to the ground; After getting pinned down by you, it's just a matter of having him stare deeply into your eyes and letting the suspension bridge effect do its thing.

But yeah, if you're sure the keys still work, making GAs normally works fine.
Otherwise, make them in one of the groups which require their members to abide by reasonable deletion requests [Lootboy SG is the most accessible one I'm aware of]. The most basic alternatives would be to either to add people directly on Steam, or to drop the key in an old giveaway of theirs

Why not this thread ?
https://www.steamgifts.com/discussion/hK2kQ/orphan-keys-drop-thread
Or at least look at it to see how others are doing (sometimes there are good ideas for dropping keys while avoiding bots).

Another solution is making GA on Indiegala. I do that when I have bad rated games or 0 CV games to give away.