3-Series BMWs are smaller, sportier, and are cheaper to maintain. They come in 2 and 4 door and, unlike the 5-series, have convertible models. If you're buying a Bimmer used and are looking for a manual transmission, it's a bit easier to find one in the 3-Series category. As the Fiver is the more luxurious, it's owners tend to lean toward an automatic transmission. Cargo room and leg room are better in the 5-Series, which will generally be more comfortable for passengers. This would be the one to get if you're looking for a family car. If, however, you want more driving pleasure and less luxury, aim for the 3. It's smaller, lighter body is more fun to drive and, again, is easier to find in manual. The Kelly Blue Book Value of a '99 5-Series is around $12-14,000. A '99 3-Series will be around $8-10,000. Pricing is usually determined by the miles on the car and it's overall condition. When it comes to making a decision between the two, it just depends on what better suits your needs and wants. The '99 530i also comes in a wagon...A plus for space and a minus for fun. I think around 2000-2001, BMW started putting navigation systems in their 5-Series. You can't find this in a 3 until really recently. As far as which is best to buy used...5-Series are much more expensive to maintain...Especially recent ones that might not be under warranty. It would be best to find a low mileage 530i if that turns out to be your choice and you don't have much in your "automobile repair fund." Personally, I'd go for a 3-Series, but that's just based on my needs and wants. One last thing to consider would be that I think that insurance for the 5 would be more than for the 3...Maybe not by too much, but it's still something to look into. That's really all I can think of right now. If you have anymore questions, feel free to ask.