Choosing a quality wetsuit is worth it's weight in gold. It should keep you warm and allow you to do dives that would be impossible or uncomfortable without thermal protection. Also having your own personal suit means that you avoid all the pitfalls of rental wetsuits - poor fit, poor condition, other peoples odours and so on.
Wetsuits must fit you well, fit is everything. A properly fitting wetsuit keeps you warm by only allowing a small layer of water into your suit and trapping it while your body heats it up to help keep you cozy. If it's too big for example then water will flow in out of the suits seals as you dive and this will not allow the suit to perform it's thermal functions.
On your new wetsuit the neck seal should be snug but not too tight. Wrist and ankle seals should lie flat against your skin and not pucker or gape as you move around. The suit should be tight, and many people forget this as they are often not used to a snug fitting suit, but not too tight. You should be able to stretch both your arms above your head and press your hands together, otherwise try the next size up. There are so many different ranges of sizes now to suit everyone with sizes like medium/small for shorter legs or medium large/tall for longer legs and so on.
It is also important to choose the right level of thermal protection for the waters you will be diving in, and yes you may need to get different suits for different times of the year or locations. A 7mm is not appropriate for the tropics or a 3mm shorty for European waters.
At temperatures of 4 to 10C you really need a drysuit. 10 to 18C a drysuit or a 7mm with extra neoprene layers like a hooded vest. 19 to 25C you are looking at a 5mm full wetsuit and at the lower end another layer of neoprene like a hooded vest would suit many people. 25 to 30C anything from a 3mm shorty or less to a 3mm full or 5mm full wetsuit will suffice for most people. For skinnier people or for those with let's say 'their own' thermal protection this could easily put you into the next lower or higher level of protection required. This can also apply to the type of climate that people come from too.
Always remember to suit up based on the water temperature at the depths you will be diving to. Surface temperatures can be 10C warmer than those at even 10 or 20m where there are thermoclines. In Cyprus many still wear drysuits until June or even July due to this. Also remember that new suits are more buoyant than an older suits as constant compression will mean that older suits will lose a bit of their buoyancy over time.
Wetsuits are like any other product - you get what you pay for. Don't go for the cheapest suit you can find. Seals and zipper design and their quality are very important for example. The more expensive they are the better quality they should be, and they will have a much better performance and reliability.
Most dive equipment manufacturers make wetsuits. The brand doesn't really matter, quality and fit are the most important factors. Although many people do favour certain brands and want to look good or professional in their suits too of course.
We hope this can help guide you when choosing your first wetsuit, buying a scuba diving wetsuit is a great first step to enhancing every dive you undertake.