@debdeb One thing not mentioned is capacity.  

If you're doing a short tour, bar bags (expandable seat bag, an under the top bar bag and a handlebar bag) should work.  Using a set of bar bags is generally for more minimalist riders.

Panniers will give you more volume for longer tours or if you prefer to pack for every contingency.  The flat space on the rack also gives you a good area for bulky items such as tents, sleeping bags, etc.  Yes, these items can be attached to the handlebar, but the extra weight in the front affects steering and the nimbleness of the bike.  Will you be comfortable with that?  Some riders are and some aren't.  Also, if you have a dropper post on your bike, an expandable seat bag will affect the full use of the dropper post.

Many tourers use panniers and a small handlebar bag for items you want quick access to such as glasses, a phone, camera, wallet, rain jacket, etc.

Good luck on your ride and be safe.

 

 

Lastly, you may find that a quality set of waterproof panniers (not water resistant) such as Ortliebs, may be cheaper than a set of quality bar bags.