Unfortunately, the cold hard reality is that it's an almost 20 year old car at this point, and things are going to break. We all deal with it here. Half the how to threads are about how to fix up old deteriorating parts.
You can actually do the subframes on jackstands too. You just have to put the stands under the axle, and under the spring buckets on the front. The problem comes when people do them on two post lifts that pick up the car from the side. The weight off the axle in the back, and the weight of the engine in the front causes the car to sag a little in the middle when you pick it up from the sides. This is true of all unibody cars. If you weld in the subframes when it's picked up like this, then the car is locked in this sagged position and your doors rub when you close them.
There are a lot of different brands of subframe connectors. As far as strength, they are all about the same. There really isn't any difference between tube steel and box steel either. A better quality manufacturer might have better fitment, and that is a consideration. Some of the people on here are really into body through subframe connectors. Personally, I think they are not worth the labor of installing. However, there are some advantages, mostly ground clearance.
Kurt
I'm new to mustangs and you guys didn't even hesitate to answer my questions that's awesome over on the chevy board all they did was make fun of people for not knowing how to do this and that I feel like were one big family on these boards and I like it lol......too bad my cars a pile of junk right now it runs and I drive it everyday but damn I'm getting sick of finding something else wrong everytime I get in the thing lol but I'm looking at it this way it would have cost me more money to put every upgrade this car has on it already then to fix a 
