A fairly recent trend is that of suspension trainers; these are not entirely new, since gymnastics rings have been in use for quite a long time, but they are still pretty new to the fitness world and even collegiate weight rooms.
There are several variations of these out there, so which should you buy? Hopefully I can help.
Gymnastics Rings are the oldest variant of suspension trainer that is out there. For a long time they only existed in gymnastics gyms and elementary school gyms covered in dust. The rise of CrossFit has really popularized ring training, and even guys like Chad Waterbury are now espousing the benefits. The best thing about rings is that they come with really long straps that are able to be hung from a ceiling. The worst thing about rings is that they have really long straps. If you're only attaching them to the top of your power rack, the rest of the straps become a huge pain in the balls. They are super comfortable for your hands, but much less comfortable if you wanted to put your feet in them for various exercises. They aren't particularly costly, with the one's listed being available for $72. I really like rings and hope to get some soon.
The TRX System is what really popularized suspension systems and remains a great product. They are very portable and very compact and extremely easy to use. They feature soft handles that are easy to grip and have loops where you can put your feet for lower body/core exercises. There is only one connection point on the TRX which makes it very quick to set up. Too, the straps are very easy to adjust the desired length. The down fall, as I see it, is that the adjustment buckles on the TRX is at the exact point where your forearms go during a suspended pushup or dips. When you do that exercise with these straps, your forearms get all sorts of fucked up and it feels miserable. It's also the most expensive system out there, with a new one being available for $189. That's a lot.
The most popular TRX copycat is the Jungle Gym XT; it is very similar to the TRX and also provides a foothold. There's not much thats bad about this piece of equipment; it's sturdy and ergonomic. I think that adjusting these straps is kind of a pain in the ass, but maybe that's just me. It's sort of just meh, and asking me to pay $79 for it is asking a lot.
Another suspension trainer that you'll see out there is the Myoforce Versus. Frankly, I think this thing sucks. They took a TRX and put a pulley on it. This way when you hold the handles, the cable is able to move back and forth. In theory it's cool and creates some sort of instability, but in reality it sucks donkey balls. We have one at my gym and I've never touched it; in fact, whenever I see it set up, I take it down. There is only one exercise that I would do with any of my clients, and it's essentially an inverted batwing row (as popularized by Dan John). It's just awkward to use and coach, and I think the negatives outweigh the benefits. I'd rather have someone get brutally strong at standard inverted rows than have use this thing. It's also painfully expensive at $169.
Lastly, my favorite suspension trainer on the market are the Blast Straps from EliteFTS. They were designed by a powerlifter for powerlifters and athletes. The handle is essentially one of the old metal D-handles that you'd see as a cable attachment at gyms and the straps are canvas webbing. These things are burly and are made to withstand a ton of use. The big bonus of these over rings is that the straps are made to be hung from a power rack, rather than a ceiling. Not a big deal. The adjustment buckle isn't super fast, but it's pretty easy to use and very simple which helps keep the cost down. The only negative of these is that you can't put your feet in them. Oh well; I don't like lower body suspension exercises anyway. I use these with my clients for suspended pushups, inverted rows and "ring" pull-ups all the time. Ben Bruno seemingly has a new use for these every month. One of the other big reasons that these are my favorite is because they only cost $50 and will last you a lifetime. Get some and use them, please.
I hope this was helpful! Have a great day and go lift some heavy shit!