The choice becomes clearer at an ordinary stop

Imagine reaching Aït Benhaddou and wanting to stay. You have taken the wide view, but the passages inside the ksar are holding your attention. On a shared tour, that interest has to fit the group's visit. On a privately planned journey, it may be possible to give it more time within the agreed route. This is where the difference becomes real.
I would begin with how you like a day to unfold. Some people feel free once someone else has settled the route. Others need their own party to shape the pace. Neither preference is a measure of how adventurous you are. It is a practical truth about what allows you to enjoy a place.
Geography still belongs in the decision. A private vehicle does not bring Merzouga closer to Marrakech or create another morning at camp. More control is useful when the itinerary makes room for what you want to change.
I would choose shared when the route already feels right
If you read a programme and recognise the places, nights and direction you want, sharing is a strong option. You do not need to pay for a different structure just because private sounds more special. There can be real pleasure in following the road with people whose reactions differ from your own.
Our three-day Merzouga routes spend the first night in the Dadès area and the second at Erg Chebbi, with a camel ride included. The return to Marrakech and continuation to Fes serve different wider holidays. I would settle that direction before worrying about which travel label sounds better.
Morocco Tour Marrakech offers daily departures, 100% guaranteed. The attraction is an organised journey you are happy to join. Its common programme is part of the agreement, and can be part of the relief too.
I would consider private when a particular need shapes the whole day
Perhaps someone in your party needs longer rests. Perhaps an architectural interest matters enough to spend much more time at one visit. Perhaps frequent hotel changes would overshadow the pleasure of travelling. In those cases, I would start by designing around the need rather than hoping a fixed group day will somehow stretch.
A privately arranged itinerary can give those priorities a better place when they are built into the plan. It still has distances, booked rooms and practical limits. Describing the actual walking, stopping and resting you need is more useful than asking for unlimited flexibility.
I would not make the decision only on the most energetic person's preferences. A journey works better when the quieter or slower member of the party can enjoy the ordinary hours too. That is where a more individual plan may earn its place.
A quieter room is not a reason to assume you need a private vehicle

Transport and accommodation solve different needs. A couple may enjoy meeting other guests on the road and still want to sleep together in a room of their own. A solo traveller may prefer single occupancy while valuing company at dinner.
State the room and tent arrangement you want for every night. At the camp, distinguish exclusive tent use from bathroom facilities. Compare those features directly rather than use shared and private as shorthand for the whole holiday.
Guiding is separate again. A driver, local guide for a cultural visit and an accompanying tour leader are different services. A private vehicle does not automatically include every guide or admission, just as a shared tour is not automatically unguided.
Compare like with like before comparing the price
A shared price is commonly presented per person, while a private quotation may be structured around your party. Read the basis of the actual offer. Comparing one solo place with a vehicle total will not show what either holiday costs you.
Match the duration, overnight stops, occupancy, meals, visits and start and end transfers. Add single-occupancy charges or separate connections where relevant. A higher figure may contain more services; a lower one may be a sensible choice if those extras are not things you need.
Do not assume that shared always means basic or that private always means luxury. Accommodation category comes from the programme. The five-day shared Marrakech–Merzouga tour, for example, describes its own stays and scheduled cultural services; these should be compared on their actual terms.
My recommendation can change halfway through your holiday
You might want independent mornings in Fes and company on the southern road. You might enjoy a shared desert journey but prefer to organise a particular city visit separately. I would allow those different wishes to coexist. A holiday does not become inconsistent because every day has not been booked in the same format.
Choose shared when the existing programme suits you and common timings feel comfortable. Consider private when the central needs of your party require a different rhythm or route. Keep room privacy, guiding and accommodation category as their own decisions.
The better choice is the one you will appreciate during the journey, not just when comparing the descriptions. Tell us what you want an ordinary day to feel like. That is where I would begin.
Explore the related guide: continuation to Fes · shared-tour experience guide · solo joining guide.
Photography credits
China Crisis · CC BY-SA 2.5 · Adapted.
Rux (Rubén Maté Lecumberri) · CC BY 2.5 · Adapted.