Question: I've got gate valves (I think that's what they're called) for all of my water shutoff valves. It's a pain to close them, and they don't quite close all the way anyway, so I was thinking of replacing them with quarter-turn ball valves. 

I have no experience soldering / sweating pipes, so would like to use compression fitting valves or threaded valves (with threaded-to-compression adapters to connect to existing copper). Is there anything wrong with this approach? Would it be acceptable for any water shutoff in the house - main, water heater, sinks, dishwasher, toilets?

Answer: 
Yes, we typically are recommending 1/4 turn ball valves for valves that are not used very often. This would include sink stops, laundry stop, and main shut off. However each of those requires a unique solution to replace them per circumstance.

The hose bibs we would not recommend a 1/4 turn ball valve as ball valves are not designed to be used often and should not outlast a globe valve which is typical on hose bibs. Also, if you have freezing temperatures at times, ball valves for hose bibs are inherently not frost free.

A push fit type fitting with rubber gasket (shark bite) for the supply side of the main shut off is generally not a good idea as they are not a very robust connection for something that is always on, does not have an easy means of shutting off (to some people), and is usually hidden. All other locations should be good for a push fit type fitting however I would not personally recommend them else where either if you can avoid them.

In general, if it is a sweated connection, I would keep it sweated or threaded; and only resort to push fit (again, shark bite style) fittings if you have to. Example would be the water is not shuf off completely with the main and city shutoffs off and you cannot get the water away from the connection long enough to sweat; in cases like these we have resorted to a push fit connection.

Also, there is another common type of connection, a compression type connection, that utilizes a brass or plastic compression piece to "squish" around the pipe and seal things; these are usually very reliable but are only readily available on certain types of valves.

For the main, I would recommend someone properly sweating in some sort of solution **even if you need to hire it out**. Many times we convert to PEX for simplicity and speed but we still sweat on the adapters on either side of the conversion.

The other locations are not typically sweated connections and should be easier for you to replace as a home owner with a good set of plumbing tools and sealants. Hose bibs many times are actually sweated and again, we sweat on an adapter farther back and usually convert to PEX.
Presumably the existing stop valves are sweated on. These valves are almost certainly the type with a rubber washer, as opposed to a gate valve. If you have no experience sweating, then you might have trouble getting them off.

If you have copper tubing water lines, you could avoid dealing with a torch by cutting off the old valves with a tubing cutter, then attaching the new ones with compression fittings. This would reduce the pipe by an inch, so you would have to have enough length to do that. Also be sure your tubing is not out of round.

You could also use valves with push on seals such as 'Sharkbite'. 

I have some experience sweating, but have gotten out of practice. I removed a sweated on stop valve on a toilet and put on a ball valve with compression fitting and ran into a little trouble. I got the old valve off easily enough, but did not wipe solder off from the copper water supply tubing. I did not detect a blob of solder which collected on the bottom of the tube with the result that the compression nut would not go on. When I finally realized what was happening I tried to reduce the blob with emery cloth with troublesome results. Finally I reheated and wiped the end of the tubing, but before I reheated I reduced the diameter off the tubing so that when I tightened down on the compression nut the fitting leaked. Finally I was able to tighten down enough to stop the leak, but the nut is or is close to being bottomed out.

I did have enough copper pipe to cut it off and place the new valve closer to the wall, but this just goes to show that a deficiency in experience and competence can lead to problems. If you decide to tackle this job yourself, start with the most accessible and least critical fixture to find out how to do it.