My first car! 57 Alpina D3 or 05 Slk 280

One of our cars is a Mercedes 200 SLK, and I must say that I don't normally like driving automatic cars, but this one is lovely.
If you're buying a second hand one, make sure that apart from the usual low mileage/service history stuff, that you get one with as many factory extras as possible already bolted on, as to put them on after you've bought one will cost a fortune.
One thing that is, in my opinion, necessary is the small glass screen that fits behind the driver and passenger heads. Without this, when the roof has done its party trick and disappeared into the boot, the wind will whip your toupee off if you go any faster than 20mph. With the rear screen, you hardly get a breeze.
A 280 (I think) is a 2.5 or 3 litre and will go like shite off a shovel. Our 200 (1.8ltr) is really surprisingly fast, and easily fast enough for all types of normal driving.
If I were you, I would investigate, maybe have a trial drive, in both SLK models before buying, as one person I have spoken to who has a 280 says that sometimes it's a bit overpowered.

Great fun car, all in all.

Your first car? Ever? Mkay..

Google will be your best friend here. Search for reliability figures and common problems for both. One may be a clear winner--though one of them being a diesel netting nearly 50mpg and big torque numbers would be intriguing to begin with.

Also be aware that a high new-price tag often brings with it much deferred maintenance. All other things being equal, go with the one with the best service history.

Finally, keep in mind that expensive car values nearly always plummet relative to their new, msrp price, and these two are no exception. Plus parts and labor are expensive, I'm gonna guess more so for the Merc.

Not knowing much about either, I'm thinking the Bimmer will be the better buy

In my area we have a company which work is to make an appraisal of the car.

This company check the car from bumper to bumper for less than $200.00.

They check mechanical and electrical, the whole vehicle, and give you the estimate of the cost of every repair needed.

They don't fix anything, they don't make money making repairs. They don't give you references for mechanic shops and their job is solely to tell you the condition of the vehicle.

If you want to buy a used car that cost you $10,000, they will tell you how much you will need additional to make the car to be fully functional.

This is a wise thing to do before buying a luxury used car. Otherwise you might experience what happened to a neighbor of mine who recently bought a 2003 Audi with less than 40,000 miles.

The car came with papers showing the replacement of the timing belt, tune ups, and so forth. This main maintenance (timing belt) was made not because the running miles but because the years of use. (Car parts and fluids decay and must be changed every 30,000-50,000 miles OR every 3-5 years).

The vehicle did run fine for two or three months. Suddenly a leak showed that the antifreeze additional container was broken, It was replaced just by buying a new one online for $35.00.

Days later, one of the pulleys stuck itself and caused the serpentine belt to break. This job required to pull the front bumper, to pull the air conditioner and radiator parts, and the replacement of the pulley and the belt.

Very soon, the tires must be replaced as well, because they still look OK but they are "dry" and won't let the vehicle to stop properly.

Plus, there are no records that the thermostat was replaced when the timing belt was changed, and the leak from the antifreeze additional container was caused by over heating.

The replacement of the thermostat in this vehicle costs $6,000 at the dealer, and about $3,000 with another mechanic, because it is a pulling out of parts like crazy.

So, be careful with what you do when you buy a used luxury car. Check the maintenance records, and figure how much will cost you to do the maintenance of the car right after you become the owner.

My neighbor is very sorry of what this used Audi vehicle is about, he didn't expect to have these problems so soon.

You better hire an expert to advice you about the extra investment that will be necessary to keep the car running and to "pass the inspection", which is mandatory in many States.

If you are not that good with car mechanics, you better start with a brand new cheap car, it won't give you the "pride" you want, but it will take you places without much maintenance. At the end, for people who don't know much mechanics, buying new cars result to be cheaper, specially with those fancy looking Hyundai, Ford, etc... which are OK as a first car.