This is a tough question. There's plenty to choose from. :P

I'd go with their early hits. It would be a toss-up between "Shoujo S" and "DOLL". If they want a live performance, I'd show them the "BEST SCANDAL 2009" DVD.

Shoujo S was the pv that struck me most
i loved the camera angles and the style of the pv
next to shoujo s would be beauteen.. i dunno why but beauteen just made a very very strong impact on me

maybe Taiyou or Namida...

but if they want it more rocking i'd show them Shoujo S, Shunkan or Nanka Buttobase.

their true rocking songs is from S.L Magic, Kagerou, Hoshi No Furu Yo Ni. but for PV i just reccomend Shunkan Sentimental, its the best PV

~>> namida no reguretto and shunkan sentimental

Video: Taiyou, BEAUTeen!!, Shunkan
Song: Kagerou, SCANDAL BABY, EVERYBODY SAY YEAH

For video: 瞬間センチメンタル, Shoujo S, 太陽と君が描くSTORY

For song: I personally like Anata ga Mawaru, of course, the 3 mentioned above as well.

I would say:
1) Shunkan Sentimental
2) Shoujo S
3) Taiyou ti Kimi ga Egaku Story

In that order

I would say shoujo s or BEAUTeen...

DOLL thru Animax Musix

song : scandal baby
pv : sakura good bye

^^

song: KOSHI-TANTAN
PV: Namida no Regret

reasons
I know KOSHI-TANTAN is a lesser known song but I find the beat very catchy :D
And I don't have to explain Namida no Regret right? I mean, hey, it's their only ballad! XD

PV: Shoujo S. Works a lot.

Song: Taiyou to kimi ga Egaku STORY I guess...

TaiKimi, Shunkan or Shoujo S

Shoujo S
And if graduation is near: Sakura Goodbye

Taiyou to kimi ga Egaku Story

everytime i show this pv to others.. they always as for more... .uhuh.

I showed the Taikimi PV to one of my doubting friends (in HD baby!) and at a "certain part" of it he went MADRE de DIOS!

The Taikimi PV is a very effective SCANDAL recruiting tool..

Shunkan sentimental
Namida no regret.

Shunkan sentimental Namida no regret (two different side of them)
.clap.

i would show shunkan sentimental :3

SONG : KOSHI TANTAN
PV : SAKURA GDBYE

I perfered:

Song ~ Yumemiru Tsubasa

PV ~ Cute .clap.

for me,Shunkan ,TaiKimi and kimi ga egaku story .happy.

song: Doll
video: in Animax Musix Fall 2010

Shoujo S
Shunkan Sentimental
Scandal Nanka Buttobase

because, in the first time i saw shunkan sentimental
i think scandal is kakkoi... .wow.