Well, it depends of what he plays with 250 pts. 250 pts means you have not much on the table and I suppose you should consider using 1 HQ & 1 troop and maybe one other thing of anything.
Battlesuits are not cheap. I would expect that he uses a commander but otherwise, if he has other battlesuits, they have a 4+ to hit usually.
You do not have choices for me. Kabalites are the main thing in Dark Eldar for shooting. Covens (Monsters/Haemonculus) and Wych Cult (Furies and melee units/Motojets) have more a melee role so its up to you.
For a first game I would take a Raider with a Disintegrator canon + 1 Archon with a Grenade Launcher and a Blaster and 5 Kabalites with a Blaster. This would make your list worth 220 pts if i am right. This would fit with the old Start Collecting Box but i think the new one has a Venom and Wych cult.
For 350 pts, add a Ravager with Disintegrator Canons....
Really, buying 10 kabalites, 1 Raider, 1 Ravagers and 1 Archon for a starter is a minimum and I thikn you will always be able to play those as they are quite good in the actual codex.