That is quite a long read. In any case, I noticed you're focused on monthly payments. It's hard to say what's the most reasonable option by comparing monthly payments alone.

Among the cars you listed, the 2009 M-Class is my favorite. There's a reason why your sisters' eyes lit up.

But you need to have more than enough to buy a luxury car. Mercedes is reliable car. However, when something happens and you need to have something changed or repaired, Mercedes parts can get really expensive.

Toyota 4Runner

or a Subaru

forget the jeeps, dodge

the Volkswagen Tiguan is nice but for that kind of money you can almost get an Acura MDX

The Problem with the STi…..Insurance will kill you. Just call and check. It has a high accident rate across the country and you have to pay. Really..I am not kidding, just call your insurance company. The car itself is safer than ANY other car you just named…But insurance will get you.

If she likes the STi….Check out the Forester XT. Turbo charged and only a BIT slower than the STi. I owned the 03 WRX and traded that car in for the 04 Forester XT. Forester was Faster and had Heated leather seats and sunroof. She may like a Forester that can beat many 2 seater sport cars. The Forester is Cheaper and insurance LOVES them.
Ofcourse Subaru = Best in snow AWD

I didn't read all that.. From what I got they both have been driving for a while…

If they are paying for the car, they should buy what they can afford…

If you are paying, they should pick the one they like best….