Welcome to scubaboard, aqua.lungs. Congratulations on deciding to make that first big purchase.
You will find that each diver or dive instructor has their own favorite brands. In reality pretty much each line is going to have their flagship products which may be lighter, longer lasting, or breath easier than "price point" (more affordable) systems. When choosing dive gear you really need to think of it as "life sustaining equipment" and thus I wouldn't recommend "going with the lowest bidder" by buying used or "gray market" stuff off the internet which may be cheaper but comes with no warranty or guarantees.
Any modern regulator, correctly maintained, is going to have a perfectly good safety record. No matter the cost, they simply will never just stop giving you air. But what will vary is the ease of breathing they offer and some of the features the regulator comes with.
I prefer piston design first stages (the bit that goes on the tank) vs. diaphragm as they usually breath easier, but they are more expensive. Rental gear usually has diaphragm first stages. The more expensive second stages (the bit that goes in your mouth) will have resistance adjustments as well as verturi switches. The resistance adjustment allows you to adjust the second stage perfectly, each dive if need be, so breathing is effortless. Not all regs have this feature. Most regs do have a venturi switch which IMO is a useless feature. ("Venturi" is a brainy word related how air and fluid flows through a space thanks to an Italian physicist of that name) It helps prevent your reg from free flowing. Just learn to manage your regs (keep them pointed down in water) and that feature is useless. My suggestion is spending more money on the first and primary second stage, then get the cheapest alternate air source as possible, or better yet get an alternate air source that is integrated into the infiltrator such as an Air II or Air Source. That will save you even more money. If you have money to burn, get titanium regs. They are light weight and will last longer than you.
With the BCD, it depends what you want to do. Most companies make travel BCD's which are just fine if you do a lot of traveling and want to save weight on your luggage. If that is not such a concern, then again, look something with a bit more features and durability. You will need to decide if you want weight integration. Most BCD's have that now. You will also need to choose between rear inflation and wrap around inflation. Rear inflation feels more awkward at the surface, always wanting to put you on your face, but most people feel they are more comfortable to swim in while on a dive as what air you may have int he BCD stays behind you keeping you in a nice position. It may be easier to float at the surface with a wrap around, but if you turn while on a dive, the air tumbles around inside and it's a little more difficult to right yourself. Not a huge issue, but a difference none the less.
Regarding yoke vs. DIN, if you are diving primarily in N. America or the tropics, get a yoke style regulator, if you are diving primarily in Europe, get a DIN. Not a big deal anyway as any shop or boat will have converters or hybrid valves on hand. If you think you might get into tech diving, get DIN.
As for specific brands and models I recommend, the Scubapro Mk25/S600 has always been my favorite and usually wins the top spot when it comes to ease of breathing, but the Aqualung Legand and the Apeks XTX200 are going to breath pretty much just as well. Another thing to consider is what brands are supported near where you live, as an anual service is strongly recommended.
