As Spiti and Ladakh Looks Alike, Many Get Confuse which one to choose. Here I am disclosing some info to help you to choose.But my personal choice is both.
Minimum time required to reach (Ex-Delhi):2 Days
Ease of Access:It takes at least 2 days to get in and 2 more to get out. The journeys are long and tiring. You'll have to reach either Manali or Shimla and change another bus/jeep to get to Spiti. From Manali, it takes a day and from Shimla, it takes 2 days by road.
Comfort Level: Low
Open Season:Technically open all year round but road blocks are common and travel within the valley is restricted during off season, which is pretty much most of the year except June to October.
Tourist Infrastructure:Minimal.There are now guesthouses/homestays in many of the major villages across Spiti but getting around isn't as easy as Ladakh. You'll have to hitchhike or walk if you don't come with your own vehicle. There's only one ATM in the valley and forget Internet while you're here.
Altitude and Acclimatization:Most of the villages in Spiti are at a height in between 3800m and 4500m, which makes acclimatization a major concern considering it is not easy to get out of the valley. Kaza is the only place that has a big hospital which proves to be inadequate most of the time since the only cure to AMS is going to lower altitude.
• In Spiti, the biggest attraction at the moment is the lack of crowd.
• Here, you can still expect to walk into a village or a food joint/cafe and strike up a conversation with fellow travellers or locals.
• The villages are much more atmospheric, accessible and picturesque.
• Highly recommended for solo/independent travellers and those who enjoy sauntering.
Kind of difficult to go offbeat in Spiti as there are not many options in the valley to be fair. But it works now because entire Spiti itself is offbeat so far, like how Ladakh was probably 10 years ago.
Any exploits to go beyond the usual path would require a lot of planning and support from locals. The valley's only artery, the national highway is limiting when it comes to exploration. However, smaller metal roads to the far flung villages of the valley can provide an exhilarating alternative to those interested in offroading.
Best suited for:Culture vultures/Independent travellers
Lakes:Dhankar Lake and Chandratal, both need hiking.Vehicles can't reach
Monasteries:Kye and Dhankar whose location and setting is unmatched!There are plenty of old monasteries in Spiti apart from these two but none as big as those in Ladakh.
Minimum time required to reach (Ex-Delhi):1hr
Ease of Access:There was once a time where reaching Leh took at least 3 days. Now all it takes is two flights from down south and you're there at the roof of the world in half a day! Also, the roads are much better compared to Spiti.
Comfort Level: High
Open Season:Open all year around thanks to flights. Within Ladakh, roads are kept open by the Indian army so you can get around easily all through the year.
Tourist Infrastructure:Well developed.All ranges of hotels/guesthouses available and it's very easy to find a shared ride to many of the famous places of Ladakh. Multi cuisine restaurants, Internet cafes, Bike/Equipment Rentals, Trek Operators etc, you have all of these in Leh.
Altitude and Acclimatization:Leh is at 3500m but all other places of interest are between 4000m and 5800m high. Acclimatization wise, Leh is a perfect base to get your body used to the low oxygen before heading into higher grounds. Evacuation out of Leh, in case of a casualty, is super convenient and there are plenty of army camps across the region to help with basic medical aid in worst case scenario.
• The variety of landscape in Ladakh is unparalleled. From shimmering blue lakes to vast plateaus to big mountains, there's plenty to see here.
• The area is so huge, you can escape the crowds easily whenever you want to.
• Brok Pa people, Islamic community, Buddhists, Changthang nomads and more. There's a huge variety in the culture as well.
• I want to add landscapes again because the,Scenery in ladakh is so epic I can't explain in words but perhaps repetition will drive home the point.
Going Offbeat:Ladakh is so vast, it's a gold mine for offbeat explorers. Beyond the well trodden paths, there's a whole other world waiting to be explored. Since it is also an army bastion, there are little traversed routes that can take you to the most remote corners of the region like Chumur, Demchok, Hanle, Chushul etc.
Ladakh is the classic case of the journey being more important that the destination. You might have seen Pangong Tso before but reaching there through Chushul/Tsaga La in Changthang or via Agham/Shyok route from Hunder is the stuff that dreams are made of!
Best suited for:Landscape lovers/Road trip aficionados
Lakes:Pangong Tso and Tso Moriri among many others. Vehicles can reach both.
P.S - Spiti's lakes are no match for these two mammoths!
Monasteries:There are more monasteries here in Ladakh than you can visit. You'll be spoilt for choice.