
There are two main choices here. You could use a hard case or go for a soft bag.
Hard Cases
They use their hardcore shell to protect from damages and have lots of padding on the insided to further ensure your bike will be found as you left it no matter what happens. They are usually expensive, large and cumbersome but on the plus side quite comfortable to move about as they always include a set of wheels to roll it. Airlines charges do vary but as a general rule you will find that a bicycle carried in this type of luggage falls into the ‘sport equipment’ extra fares when they apply them, otherwise you will simply pay more due to the weight but also the size of the package as your luggage will often have to be checked in at special gates for Extra Large items. They do not have much space left for anything else beyond the bike. This means that you will have to carry much more weight in the cabin. Often airlines will not let you bring more than one bag for example and will also want to know the weight. You see where this is going. Yet again more charges as well as losing your patience in stressful negotiations!
As far as affecting what kind of tour you will be able to have, a hard case poses a practical problem too. You will have to store it somewhere when you start touring. A tour from point A to point B will only be possible if you take some transportation to return to the starting point when you have completed your journey.
Provided the above conditions are not too limiting, a hard case ensures that your bike will be safe and undamaged.
Soft Bags
Especially when traveling by airplane, they are not as good as hard cases in protecting your bicycle. On the other hand they give you all the freedom to decide where to stay and how to travel. As they are light and can be folded small and carried as part of your luggage you will also have the ability to use them should you need to take some transportation in the middle of a tour. You can find an effective bag for not much more than it would cost to buy a cup of coffee and being light, they limit the chances of you having to pay any extra fees during transport.
The last thing we want as touring cyclists is to realise that our bike was damaged during transport. With a soft bag you have to put some extra attention and care in how you are packing. Put soft items all around the bike, and include further padding at the bottom. Another good idea is to insert some cardboard that you can cut down to size and can become another layer that can protect the bike further.
Soft cases are all that I have used for all my touring travel. Experience taught me how to compensate for their vulnerability with some of the ideas that you have just read and more that you will be able to see from my videos on the subject.