First off, active PFC is not new, it has been around for long enough it shouldn't be a marketing point anymore, which also means if you stumble across a unit without it then you found an ancient unit or a unit they really cheaped out on. The implementation of APFC in PSUs comes with the advantage of being able to accept any input voltage and frequency which means that a PSU sold in Germany will work in Canada or Japan without issue, so you can easily tell a unit does not have APFC if it still has the little red voltage switch. APFC does not provide any significant change to efficiency or any other aspect of a PSU.
If you are curious what APFC does, it makes the complicated electronic load of your PSU look more like the simple load of a toaster. If you are in North America and on residential power, you don't care about the power factor of your load, other countries however are billed for it so it does reduce their power bills, and more importantly significantly reduces load on the utilities.
12V rails - Multiple or single?
This is a tricky one to explain so check out the post below that goes into far more detail, but in short, it doesn't matter! Just make sure that the combined 12V rail capacity is enough to run the hardware you want.
Efficiency and 80 Plus Certifications
There are two important things to know about 80 Plus certifications. First, it wasn't meant for the consumer, it was meant for the commercial environment which has hundreds or thousands of computers in a building and was supposed to dramatically decrease the load on the utilities companies. Second, 80 plus certifications are not correlated with build quality or performance, an 80 plus gold unit isn't necessarily better than an 80 plus bronze unit, it is just more efficient, it could perform better or worse, but the 80+ certification won't tell you that.
PSU efficiency does matter to you though, it will save you small amounts of money per year if you have a higher efficiency PSU, and it will also reduce the heat generated by your PSU, but this is fairly insignificant for a single computer and much more significant for commercial spaces with hundreds or thousands of computers.
For more information on PSU efficiency myths and 80+ certifications refer to this post
Modular, Semi-modular, or non-modular
This is really a matter of personal preference. Semi modular PSUs have some cables permanently attached like the 24 pin and 8 pin CPU cable since you will always use these cables, most of the rest can be detached. On a modular power supply all of the cables can be detached, while a non-modular all of the cables are permanently attached. Modular PSUs make cable management a little easier and free up some space in your case, so if you have a case with a window you might like the modular PSU to keep it looking nicer, but modular/semi-modular/non-modular has no effect on the performance of the PSU.
PSUs split the power into multiple "rails", the +12V rail is the main while the +5V and +3.3V rails are the minor rails. Modern computers pull ~80% of their power from the 12V rail since the GPU and CPU are both powered by this rail, older PSUs have less power on the +12V rail and have more on their +5V and +3.3V rails as the CPU used to be power from the +5V rail. Make sure any PSU you are buying for a modern system has most of its power available on the +12V rail.
Below you will see the load table sticker from a Corsair HX750, a modern PSU which has most of its capacity available to you on the 12V rail where you need it
And below you will see the load table from an old logisys unit that has been rebadged and pretends to be meant for a modern system, but it has more power on the minor rails than the HX750 does, and only has 300 of its 550W available on the 12V rail which tell you that it is from an older age when the CPU was on the 5V rail, you don't want to use a unit from this era to power a modern PC.