Choose self-guided when
The route is waymarked and well travelled, you can navigate in poor visibility, and you are comfortable judging weather and turning back.
You want maximum flexibility and the lowest cost, and you are prepared to book huts months ahead yourself.
Choose guided when
The route involves glaciers, rope work, via ferrata or serious exposure.
You are new to the range, travelling solo, or hiking with mixed-ability companions.
You want local knowledge — the alternative valley when the forecast turns, the hut that still has beds, the path that avoids the crowds.
Related questions
Is a guide required by law?
Rarely for hiking. A few protected areas and specific peaks require a licensed guide, but in most of Europe it is a safety and quality decision rather than a legal one.