Caulking doesn't need to be complicated.
Life seemed much simpler when the hardware store carried only three kinds of caulk. Now, home centers dedicate an entire aisle to caulk. As a result, confusion reigns when it's time to do a very simple job.
But I don't think caulking needs to be that complicated. Other than specialized caulk for specific tasks, like patching gutters, I've found that a high-quality siliconized acrylic-latex caulk is an excellent choice for almost all interior and exterior uses. That's what my crews use most of the time.
I know people who have paid $5 to $6 per tube for 100 percent silicone caulk and filled every crevice and seam they could find. It was only at the end of the job that they discovered that paint won't stick to silicone caulk. They were left with a job that could have looked much better. On the other hand, acrylic-latex caulk can be painted, cleans up with water and is almost half the price of 100 percent silicone.
But there are a few exceptions to that rule. You should use silicone tub-and-tile caulk in the bathroom because it resists mildew and doesn't shrink. For gaps of 1/4 in. or more, or where the caulk must join dissimilar materials, use urethane caulk because it's more elastic. For joints more than 3/8 in. wide, pack the crack with foam backer rod before applying caulk so the seam won't crack later. And bridge gaps up to 1 in. with a combination of backer rod and urethane caulk, but don't try to caulk anything wider than that.
When applying caulk, more is not always better. If you apply too much caulk to a joint and then smooth it out with a finger, the caulk tends to spread onto adjoining surfaces. This is just plain unattractive. And outdoors, this thin layer of caulk will weather differently than the rest of the seam. Getting an even bead of caulk is easier with a high-quality caulk gun, so skip the 99-cent special. Just remember to cut off the plastic tip at a 45-degree angle, which will help you apply the caulk evenly. Another tip: Take advantage of the many colors that caulk now comes in. They help paint cover much better than regular old white.
Besides caulking around tubs and sinks (where you are protecting against water damage), don't forget to seal around window and doors, and any crack that leads to the outside. I tell people that if they were to add up all the cracks and holes in a typical 20-year-old house, it would amount to a 3x3-ft. space, which would be just like leaving a window open all the time.