I'm saying this as someone who has done their research, as well as some testing. All steps of the scientific method were utilized, is what I'm saying—especially the experimental step.
Saliva—it works enough to start some light penetration, but obviously you must be sure to get your own naughty juices flowing shortly afterward. It dries quickly, but at least it's all-natural and always at one's disposal. This is probably an obvious point to make. Let's be honest and admit that many times, saliva will not suffice.
Now, there are some great water-based lubes out there. I would not KY on that list. Of course it is more readily available at any grocery or drug store, and usually more affordable than many other lubricant choices. However, not only does it not stand the test of time (like if you're planning on having more than just a quickie), it leaves a weird residue. It is sticky, and is uncomfortable to try to sleep after use without washing it off. Pro: it washes off easily, and can be useful for short sexy time sessions. In my opinion, this particular wannabe sex serum should stay in hospitals where it belongs. Side note: I am also quite close to a person who is allergic to KY, and the moment this person found out, it was a bit of a traumatizing situation. Luckily an allergy to KY is not common.
The pricier water-based lubricants found online and at adult stores are better. Most of the time they are fine for long term fornication, but some still leave an odd stickiness after the fact. Fuck Water is a lovely option (it does not leave much of a residue, if at all), though it is around $17.00 for an 8 ounce bottle. To be fair though, you do not need to use much of it to get the job done, so it isn't like you'll go through a bottle quickly. Its texture is similar to cold baby batter, and it looks like it too. Fuck Water, and really any water-based lubricants are perfect for use with condoms—just remember not to skimp on your water-based investment, as you usually get what you pay for.
Silicone-based lubricants are pretty rad, for multiple orifices. The pros include that they are resilient, they are less likely to cause an allergic reaction, and can be used with latex protection mechanisms. The cons: they are not recommended for use with sex toys since they are long-lasting and may not wash off well enough to prevent from bacteria growth. Often, they leave a sticky residue like water-based lubes, but more difficult to get rid of. An example of a common silicone-based lube: Astroglide.
I've dabbled in using household cooking oils, and I'm not ashamed to say so. However, do NOT use any oil-based lubricants with condoms or dental dams. Oils are known to breakdown latex and causes leaks or breaks, which would defeat the purpose of using a latex protective measure in the first place. So, if you would like to use olive oil or coconut oil (I prefer the latter due to taste, smell, and the fact that it is lighter), use a non-latex condom. If you're going without a barrier, be safe and do it in a monogamous relationship. Oils do not dry quickly, so they do allow for a long game of hiding the sausage. On the flipside, oils sometimes clog pores or (though less likely) cause an infection. Be careful where you're dripping these types of lubricants too, because they easily stain sheets. Full disclosure, I have not experienced any of the downsides of coconut oil.
Only you and your partner know what product is best for your sex life. I'm just here to give some tips and testimonies.