Regulators - Buy a brand carried by a local dive shop that is a authorized dealer and service center for that brand. Having said that a environmentally sealed cold water first stage regulator will be reliable under all conditions. My own preference brand is Oceanic which also which is American Underwater Products and they also manufacture Aeris and Hollis brands. Other quality regs are made by Atomic, Aqua-Lung, Scubapro and Sherwood. I suggest these because they are brands that are common worldwide which gives you a better chance to get service in the event of a failure during a trip.
As for BCD the same can be said about brand choice however failures are much more rare and more likely to be user serviceable with common parts. So the issue becomes what will suit your diving. Do you need pockets to store extra gear? Do you want a more minimalist approach? Jacket style, Back Plate & Wing or Side Mounts? When talking about a Jacket Style BCD this is the most common in use today but come in 2 types Standard jacket or Back Inflator style. Both are available as weight integrated and may have additional storage pockets. The back inflator in many circles is considered the next stage design as it’s a compromise to that of the Back Plate & Wing. It’s characteristics in the water are similar in that while diving it tends to keep the diver in a more horizontal swimming position. On the surface it is important to only inflate enough to float the divers head. Overinflating can cause a diver to be forced forward doing a face plant into the water with either the Back inflator jacket or the BP&W where the standard jacket can raise the diver further out of the water. (proper form is to just inflate to float the head) The BP&W has a few advantages over the jacket. It creates a more stable platform to mount the tank giving a more secure feeling. It’s a modular system that allows using plates of differing materials and weights that aid in weighting and trim. It allows for a choice of different weighting systems besides the inherent weight of the plate. It allows for different wings with various lift capacities this allows the diver to carry greater loads of equipment such as rebreathers and multiple tanks. This is an advanced system that is used by recreational divers and technical divers alike and in fact would allow you to advance into tec diving should you want to in the future. Side mounts are a newer entry where the tanks and regulators are attached to you in such a way as to allow better flexibility and movement. It has it’s start in cave diving but has been making inroads to recreational diving. Since I have no direct experience with it I’ll leave further comment on it to someone who does.