Join the club. I couldn't decide between them, so I bought both :lol: I will mostly likely be sticking with the Nexus 5, primarily because it's lighter and smaller, has more accessories, receives updates quickly and is a bit nicer to hold. I'm a fairly light user, so the battery lasts me around 2 days. The G2 will get to 2.5-3 days on light use with relative ease. I don't feel like I can be bothered with custom ROMs.
I don't use the camera much, but the G2's camera is usually better except for the fact that the stock software tends to keep the shutter open too long and this makes low light photos a bit blurry. There's a modded version on xda-developers that tweaks the software and supposedly improves this, though I haven't used it myself. It appears as though the N5 reproduces the colour of objects in the photo more accurately, but that's most likely down to the display (I've not compared them on the same screen). Regardless of its flaws, the LG camera software is simply better than the AOSP one in almost every way, and yes, that's taking into consideration the 4.4.2 update.
The N5 has a more accurate display with average-at-best contrast (blacks are charcoal) while the G2 is oversaturated and has a cooler white point and much stronger contrast. You will be at home with the G2's display if you've come from Samsung's eye-bleeding AMOLED displays.
The G2 has a greasy back. I think it is more grippy in the hand than the N5 despite popular opinion, but it's awful nonetheless. Get a case and the problem is solved, though you'll have a larger and heavier device if that concerns you. A TPU case will significantly improve the usability of the G2 while lying on a hard surface too, as it slips very easily compared to when it's in the hand.
If you are into glass screen protectors you'll find that there are some which are incompatible with the G2 despite being designed for it. Many have resolved problems with their initial batches though. The issue is that the G2's glass has a tapered edge and this means that thick pieces of glass tend not to stick around the edges. The good ones are all cut small so that they don't cover the tapered area and then peal. Might not be an issue for film SPs since they're much thinner.
Knock on is cool. I like being able to check the time without having to abuse the power button. Definite plus for the G2, and necessary given that the power button is on the back. I'm not a fan or a hater of the back buttons. They're a bit weird, but at least you don't keep pressing them when picking up the phone.
G2 has an IR blaster. If you want to use your phone as a remote then the N5 won't do you any good. A bit gimmicky but it has its uses.
Stock Android is faster and smoother. There is simply no getting around the fact that LG burdened their phone with a huge amount of software and this hampers it. It's not night and day, but you can easily tell the difference. Worse still is that the LG skin is trying too much to be like Touchwiz. The notifications screen has almost no room for notifications. Most issues can be resolved with custom ROMs or by rooting and modifying the stock ROM, with the latter possibly being preferable because the LG camera software is far better than the AOSP one.
What else have I not incoherently rambled about.... hmm... the G2 comes with earphones, or at least mine did. I've not used them, but they're supposedly pretty decent. G2 has a slightly better speaker, and can get louder out of the box. The G2 creaks a little when stressed, while the N5 does not, giving it a slightly less sturdy feeling.