Is the whip the best weapon for the bladesinger? No doubt the damage is only 1D4, but with it's one handed, finesse and reach property(10feet), it pairs beautifully with booming blade. 

For the most part, we don't always want a bladesinger to necessarily engage in melee, but when it does, it does rely on booming blade to do most of the damage anyways, not the weapon damage. 

The problem is that it doesn't necessarily pair with booming blade. At least not the reach part. The spell specifies 5'. DM may rule otherwise.

If you go with Haste as your Concentration spell, three attacks a round encourage you to go with larger hit dice. 

In any case, The "best" weapon is generally going to be whatever you find as a magic weapon. 

You know what is a surprisingly good weapon for Bladesingers? Net paired with True Strike. Free restrain.

Quote from Mephista >>

The problem is that it doesn't necessarily pair with booming blade. At least not the reach part. The spell specifies 5'. DM may rule otherwise.

If you go with Haste as your Concentration spell, three attacks a round encourage you to go with larger hit dice. 

In any case, The "best" weapon is generally going to be whatever you find as a magic weapon. 

 Good point. I thought that with the change to spell as "Self", i could use any melee weapon. Didn't see the second restriction 

I still am not sure True Strike is good in this case. You still have to wait until your next turn before you get advantage on the attack roll. If True Strike instead affected the next weapon attack made, then I could see it working really well for Bladesingers and Eldritch Knights. 

Unless I am missing something, the True Strike + Net combo doesnt seem great since it requires two rounds (even if you do still get to make an attack the same turn you cast True Strike). Also, I do not remember if Nets require two hands to throw, but if it does then throwing it might also risk ending your bladesong.

So like, use true strike round 1, maintain concentration, then throw the net round 2? I’d rather just throw the net and skip true strike.

Well you guys are correct. Man... True Strike is just AWFUL.

Tbh, shoving prone and then throwing the net (starting at level 5) would be far superior to true strike + net.

As far as OP's original question goes, I would say shortsword/scimitar + hand crossbow with crossbow expert is pretty darn good.

I like the whip...elves already get shortswords so you can fall back on that if you find a nice weapon...if you dual wield later having a whip and a shortsword is better than just one...

Whips and Spirit Shroud ftw

No the real trick is to take Warcaster and the whip. Then you have a much larger area where you can have enemies trigger opportunity attacks... which you convert into spells. Bonus: because theyre 10ft away when triggered these can be ranged spells not at disadvantage like normal op attacks from melee range weapons. Extra extra bonus... you dont even need whip proficiency to do this.

Added triple bonus, you can still hold your rapier/shadowblade in the other hand and use it to do most of your attacking, anyway.

So you can choose to op attack as they leave 5ft away or 10ft away. Based on what spell you wanna cast at them.

Gonna disagree here. I'm not trying to tank. I want them to stay away.

Here was my thought....

- Slasher feat drops their speed by 10 ft on hit

- 2nd attack Ray of frost drops their speed by 10 ft.

- Starting their turn in Spirit Shroud drops their speed by 10 ft. SS also helps with your damage

For a lot of npcs, this means that they aren't moving. Add to that hijinks creating difficult terrain and you've got kind of a cool niche character.

Quote from gilgamesh1973 >>

 Good point. I thought that with the change to spell as "Self", i could use any melee weapon. Didn't see the second restriction 

Spell Sniper feat, doubles the range of booming blade and green flame blade to 10', war caster feat then you can booming blade someone who runs away .... BOOM!

There are ways to get hex or hunters mark also, add eldritch claw tattoos ... the d4 then becomes 1d4 + 2d6 + booming blade.