Hello!
Best first Luger advice: don't just buy the first one you see!

I would strongly recommend joining up at the Luger forum. LOTS of very valuable information! The classified ads there are a good way to buy a Luger as the members are very honest and will help guide you for your first purchase.
Also, I would recommend buying a few books on the Luger history and variations. I read several books over the course of a year before making my first Luger buy. I'm glad I did it that way!

For German made ones, I like the DWM ones best. They are very nicely made, and were made in enough numbers that can get the best ratio of "dollar spent to condition received".
But, my overall favorites are the Swiss made ones. They tend to be in very fine condition, and they tend to shoot very, very well.
But, they will almost all be in 7.65mm. So, your preference might well be different.

Lugers are very fascinating! Enjoy the process of researching the subject, and you are bound to get a bigger thrill and appreciation when you make that first score!

Best Regards,
Jim