Close call this one, Stargazer! Both are great games from one of pinball's finest years: 1981. You can't go wrong with either, gameplay-wise. Great rulesets which are pretty complicated considered the time they were made.
Most Lightnings have bad playfield inserts. The two large blue ones are usually the worst, and are not readily available. Also check if the speech is working. The classic Stern speech chip is very hard to find.
Lots of Elektra's have bad upper playfields. Also, when you shop it: The entire main playfield is covered by a plexiglass. Be careful when you take the plexiglass off. It may take some of the playfield artwork with it!
I would normally say you are more than welcome to try my restored and clearcoated Lightning out, but it's staying over at my brother in Groningen at the moment.
If you decide not to take the Elektra, let me know! I'm interested in owning one once again.