Howdy Mr. Dean1818,
I think it really depends on what use you to intend to make with the ammo, more than anything else.
If you are just going to punch holes in paper, then I would say buy whichever weight bullet you can get the best price/deal on, and don't worry what grain it is.
If you are going to use it for self-defense purposes, then I would suggest you choose a JHP projectile. With a SD load I think it really comes down more to one of personal preference in choosing between the 165 and 180 grain projectiles, at least in my view.
As a reloader, I know that with the lighter projectile, you can safely use a bit more powder, and obtain slightly higher muzzle velocity. Of course that statement is true of any caliber projectile, not just the .40 rounds.
If you were looking at a .38spc/.357mag load, the difference between say a 110 or 125 and the 158, or even in 9mm the difference between a 115 and a 147 would be much more extreme, than between these two weights in .40.
As a general rule, the higher the muzzle velocity, the more reliable expansion you can expect from that JHP - within limits. But with the .40 cal 165 and 180, I feel it is much more an issue of bullet brand that will determine your likely expansion. Which I reckon is a fancy way of saying some brands/designs simply tend to be a bit more reliable expanders than do others.
My agency was lucky enough to hire a retired ballistican from H.P. White Laboratories, who had grown bored with sitting around his house. He because our first "true" ballistics expert in my mind. Among his duties were the selection of various duty and practice rounds my agency would purchase with government funds.
Mr. Jim evaluated all of the various brands of JHP ammo that was available at that point in time (mid 90s or so), and made his choices based on his testing of the actual rounds. In handgun JHP ammo, he was very impressed with both the Speer Gold Dot and the Remington Golden Saber. In 9mm he selected the Gold Dot as our primary issue round, with the Golden Saber available for issued handguns that did not like the Gold Dot.
In .40 he chose both the 165 Gold Dot and the Winchester 165 SXT. I have some of both loads in my ammo cabinet. I should also point out that not all bullets weights are created equally. By that I mean if you were to mix up Gold Dot and SXT .40s in a mag, you would likely notice a real difference in felt recoil while shooting them. To me the Gold Dot is a hotter/harsher recoiling round than is the SXT. My chronograph work has also shown that the Gold Dot has a higher MV than the SXT.
But faster is not always better too in my view. What is much more important to me than pure MV is how well or poorly a specific load shoots in my handguns, and how well I shoot it as well. I have some medical issues, which can cause shooting to stop being fun quickly with some rounds these days. When I am carrying a .40 as a self defense weapon, my choice to to chamber a Gold Dot and have the first two rounds in the mag be Gold Dots. The remainder of the mag and all of my spare mags are loaded with SXT rounds. I do this because if I needed to fired an extended number of rounds, I know from personal experience I can fire the SXT more accurately and quicker than I can fire the Gold Dot. Both rounds are extremely accurate in my handguns, and I have confidence in both rounds. I just make this choice, because for me it seems to work best.
To me after I have established a self defense load will fire reliably in a handgun, and gives me consistent POA-POI, then I simply go with the round I feel I can fire the most accurately in combat style shooting.
But what works for me may not work for the next person that tried that combination either. So I always suggest that everyone do their own testing in their firearms, and then make their own personal choices as to what rounds they should trust their lives to.
But with the slight difference in weight between the 165 and 180 in .40 ammo, while I lean towards the 165, I would not feel poorely armed with a 180 load either.
Hope this at least gives you some things to consider, but it is not a definitive answer for sure. I am simply not sure there really is one to your question to be candid. Go with what works the best for you in your pistols.