Well, as far as which is a better deal, that depends on a lot. If the 3 series is a really nice 328ic with low miles, and you like convertibles, and the 5 series is a decent 525 with average miles, it's a pretty easy decision. Basically, if you like a larger sport sedan that can seat 4 comfortably, and 5 with a slight sacrifice of comfort for the rear passengers, go with the 5 series. If you want a smaller sport sedan that is usually a little bit cheaper, but will only really fit two people comfortably (Rear leg space), but is also lighter, and has more aftermarket support available, go with the 3 series. Now that being said, if you could find a pair of Bimmers for let's say $10,000 (No comments on my dream world now), and the choice was between a 1998 328is with 50,000 miles, a nice set of wheels, some coilovers, a few doodads under the hood to spice things up, and nice air freshener, and a 1998 540i with 75,000 miles, a really nice interior, some cool wheels, a few more doodads under the hood, a set of upgraded shocks and springs, and the exterior looked mint, I would go with the 540i. Nice 4 liter V8 power in a very comfortable sedan that would be good for a young family if the need should arise. The value would be better on the 5 series, but the 3 series is a slightly sportier car, and the amount of aftermarket support for the 3 seires is almost unbelievable. But this is just my opinion. What exactly are you looking for in your BMW purchase?