The best golf club travel company is "Club Glove." The pros swear by it. It sells a burst-proof bag that has a lifetime guarantee. If you're flying, you need this bag.
Avoid them if possible. When traveling, you don't know how your clubs will be moved and shifted with other luggage. Hard cases tend to break easier when mixed with other items. A soft case will absorb blows and be more durable in the long run.
FedEx has been known to ship anything, especially golf clubs. You don't even need to put the clubs in a box. If you have a travel bag, you can put the sticker on it or wrap it around the handle with the plastic adhesive packing slip sleeve, and it will deliver it. UPS will do the same.
If you need to mail clubs in a box, go to a store that sells golf clubs. It will have boxes from shipments it will throw away or give to customers for free. Do not try to make your own box from other boxes. Wrap the club heads in newspaper or bubble wrap to insulate them. Evenly weight the box so the distribution is not shifted to one side that would make it top heavy. Fill the remaining space with paper. Make sure nothing can move and the contents are secure. Shake it violently to check how it will handle. Tape the box and be sure to cover any openings so water and moisture can't get in.