Alot of people answering so far that seem to have little to no idea what car you are talking about, or have it mixed up with the 924 (which was originally designed for Audi and used many Audi parts). The race version of the 924, which was the 924 GTS served as the basic guide for the creation of the 944... so with that out of the way:
The 944 is a pretty good car. It's well engineered, has excellent build quality, offers good reliability, and decent performance. On the downside, while these cars are now available at some very inexpensive prices, upkeep and repairs will be more represenative of the fact that this was a fairly expensive car when it was introduced. While reliable, repairs will eventually happen (these are 20+ year old cars now). And while it offers decent performance (great performance in terms of balance and handling and braking), it is not a fast car, and any designs you might have to make it so will quickly exceed it's value and make it much less costly to simply buy a different car. And due to it's potential to be a costly car to repair, if you are stretching to afford this, you would be much better off to wait until you have more money to spend on a car and revisit Porsches at that time.
The Turbo (951) is more desirable and more expensive than the normally asperated version. Unlike the base 944, this car does offer many upgrade paths and is much quicker even in factory trim. However it will have a higher cost of ownership. In general, performance goes up in both the 944 and 951 as the series went on, with early 944 models offering the lowest levels of performance and later models like the 944S2 offering the most (or the later 944 Turbo S being the best among the 951 models).
As with any used Porsche, finding a good well maintained example is the best way to avoid substantial costs down the road (the often expressed "the most expensive Porsche you can buy is a cheap one" is very true). Become familar with the cars and make sure you have a knowledgable Porsche mechanic that can do a pre-purchase inspection.
Also, while low mileage cars are generally considered desirable, I'd add a word of warning - unless you are buying this to be a seldomly driven collector car or conours car, avoid very low mileage cars. A car with only 20k that is now 20 years old has not been driven often! Cars in general, and Porsches especially were designed to be driven. In not, many parts and seals that were designed to be lubricated through normal use will have worn and dried out. Everything may seem normal, at least until put into regular service, where upon part after part after part will start to fail and need to be replaced. In my experience, for a car that is to be driven, a high mileage example will be more reliable than a low... more attention should be paid to the condition of the car, it's service history, and the results of the pre-purchase inspection than it's mileage.