The main reasons to want a riding suit are for protection in case of a fall; because they are substantially (but not perfectly) waterproof; and because the good ones go on and off quickly. So, you can put on your work clothes, put a riding suit on over your work clothes in about 30 seconds, drive to work in pretty much any temperature from about 45° to 90°, rain or shine, and get there in decent shape. It then takes about 30 seconds to remove the riding suit.
Riding suits are not so comfortable when the temperature is above about 90°, depending on your personal tolerance for heat, and you need additional layers if you're going to spend significant time riding in temperatures below about 45°, depending on your personal tolerance for cold. Most people seem to prefer the two piece suits for the added versatility. Riding pants are generally uncomfortable to wear above about 85°, again depending on your personal tolerance for heat weighed against your fear of road rash.
Whatever you buy, it's important it be comfortable or you won't want to wear it. The Aerostitch people will work with you until you are happy. The other products have to fit off the rack, so it's important you try them on before buying. Particularly the one piece suits, where if your body dimensions are at all unusual they will not be a good fit. I, for example, cannot wear a Firstgear one piece because when the top fits me, the legs are too long.
For rain suits, the unfortunate reality is that the cheaper and uglier the rain suit, the better it works. The yellow "mushroom" suits that crossing guards wear made out of non-breathing PVC will keep you really dry. If it's above about 80° they will also roast you to medium well. The "best" suits all eventually collect some water inside which works its way down to your crotch, or if it's a gore-tex breathing type of suit, it will eventually let in water that inevitably pools at your crotch. Sorry. Think of it not as a bug, but rather as a design feature: it's a built-in birth control accessory.
If your only purpose for riding pants is to stay warm, you won't need them in temperatures above about 55°. Below 55° you can get a pair of ski pants on sale at any sporting goods store for about $25 which work at least as well as everything here for keeping you warm.
There are no leather suits here. Leather is very nice to look at, and it's the best stuff to be wearing if you're going to fall down, but it is not very warm in the winter and it is extremely hot in the summer. It's also hard to make leather get and stay waterproof. If you want leather, the best leather is available at Harley dealers, Fieldshear and Hein Gericke.
There are numerous stories on the internet of people falling down in all of the products below and walking away unscathed. Aerostitch stands out after a crash in repairing or replacing their garments at reasonable prices. It's moderately likely that after a significant crash you would have to replace the other products here.
Generally speaking, the Aerostitch products do not seal against wind, but seal reasonably well against rain. For this reason they're comfortable into the low 90s. However, somewhere in the mid-60's you're likely to want to put on the liner or a sweatshirt or something. Aerostitch suits are, as the brits say, 'quite dear.' Their pricing is 25% - 50% higher than anyone else. The AlpineStar, Belstaff and Kilimanjaro are both reputed to be more waterproof than the Aerostitch. Belstaff invented motorcycle riding gear, and they remain one of the very best manufacturers. They're in the UK, so availability in the US is spotty. The Kilimanjaro has the best venting, and is therefore comfortable at higher temperatures than the Aerostitch or Belstaff. Unfortunately, the Kilimanjaro has a completely inadequate liner, and because of this is pretty much useless below about 40°.
There is a European body called CE which makes standards for vehicles, much like our DOT. They have a standard for motorcycle clothing and protective armor. All of the suits below which feature armor are CE certified. CE armor is good stuff for protecting you in a slide, or from small impacts.
People seem to focus on the injury caused by the slide. This is not where you tend to get hurt. On a taller bike like a touring or sport touring bike, you get hurt more from the fall. The bike is tipping over at 1g, but that number relates to the bike's center of mass. Your shoulders are about three times as high up as the center of mass, so you're actually levered into the ground at 2 to 3 gs, which means the fall from like 3-5 feet above the ground is effectively more like a fall from 6-15 feet above the ground. Leather and CE padding aren't going to have much effect on this.
You see these films where GP racers go down at 100 mph and walk away. It's worthwhile to remember that they are falling from only a foot or so high - often their knee is already on the pavement, and their elbows are only a few inches up. It's only a slide, and leather handles that just great.
There are summer-only jackets which are thin and highly perforated for ventilation, and have the CE armor. The most popular are the Firstgear Mesh Tex and the Joe Rocket Phoenix. Pictures and prices below. Although it's more money, if you want to ride in armor all year round, I suggest you consider a warmer jacket for October through May, and a mesh jacket for June through September. I don't believe there is a single jacket that's waterproof and warm enough for winter, and sufficiently vented to use in summer.
There are a lot of reviews of the following products at MotorcycleGearReview.com. Unfortunately the reviews were mostly written by people who have only owned one or two products, so they are not so good at comparisons.
Many of the manufacturers below make lower price products. Generally I have shown only the top of the line, and then found the best price on it. One can get something for perhaps $100 less by giving up some features. To quote long distance rider Ray Stevens, "Buy the best and just cry once."