Sometimes you just feel the need to build and for whatever reason if you simply can't get your hands on physical LEGO bricks for an idea you have in mind, don't worry, there are some great digital software out there to choose from to satisfy your building need. There's a huge set of differences once you dive deeper - this is an introductory guide for you to decide on what to get started with and a quick comparison.
Although you have free access to both, it can be hard to distinguish between them and know which one is more suited to you. So this article should help you decide; LEGO Digital Designer or Stu.io?
Origins
First lets talk about their origins. LEGO Digital Designer or LDD for short is directly affiliated with The LEGO Group. This used to be the only design software out there, and an old feature was that you could order you model, and the bricks would be delivered to you. However, after surviving for 6 years, The LEGO Group had this to say: "it has struggled to live up to the quality standards for a LEGO service. As a result, the LEGO® Design byME service was closed in January 2012".
On the other hand, Stud.io was developed by Bricklink, a huge online brick store which is often called the unofficial LEGO marketplace because of how easy it is to order bricks. The software is directly affiliated with Bricklink and therefore receives all the latest bricks and updates. So let's get into which one is better suited to you as a builder and designer.
LEGO LDD Interface
Easy of use
Let's talk ease of use. LDD, as mentioned, has not been updated as frequently ever since its orders have collapsed, and therefore does not run as smoothly as Stud.io. Although it can crash and lag, it is an excellent choice in terms of simplicity. Everything is set out in clear menus and locations, with easy controls and features which make it perfect for first time users. Stud.io on the other hand runs smoother in general but takes time to get the hang off. This is because you can do lots more things with it, such as check the weight and price of pieces to name just a few.
Which beings us on nicely to our next topic; features. LDD is very basic in terms of features, but has some useful functions such as instructions for your model and the ability to change colour, hinge and flex parts as well as all the general ones such as copy, paste extra. Now this list is smashed out of the park with Stud.io, as you have access to a whole host of features. You can view the specifications of the build, such as weight and price, render your build easily with a built in software, export directly into Bricklink, import official LEGO sets as well as all the features LDD has. So in terms of features, the point goes to Stud.io as you have access to a wide range of features that aid and speed up the designing process, while being fairly easy to use.
Stud.io Interface
A negative for both is the ease of navigation. There is a simple search bar for both, but you have to by very specific to get what you want. From personal experience, it is easiest to search for the size of the piece, such as 1x4. However, if you are looking for an unusual piece, the chances are it has a weird and wacky name. This requires experience in the software for navigation, and the best place to practice is with LDD, because of its simple menus, so it wins in this topic.
Another point worth mentioning is the 2 mode available in LDD. The first gives you access to all the parts that are available and have been produced. The second is called Unlimited, because you can make any part any colour you wish. This is highly beneficial for builders that just want to experiment and enjoy themselves but won't build the model in the physical world. Stud.io does not have this feature and therefore is better for those wishing to just plan their build, then order the bricks to build it. This is aided by the direct link to Bricklink, allowing you to buy the bricks and see what is available. It is also great to see the weight and any possible collisions you might encounter; making Stud.io the best for a practical and professional builder.
Rendering
If you plan to render your build, which is to create a final image of your build, LDD provides a rudimentary output, almost like a screenshot based on your screen resolution setting. You can actually do a better job but it's a two step process - taking your file and using it on a standalone rendered like LDD 2 POV-Ray or Bluerender which can deliver exceptional results. Stud.io comes built in eliminating that two step process with a slightly better renderer that can give you decent results.
The left image is rendered with LDD whilst the right is Stud.io. You can see that there are shadows (underneath the Snow Speeder) , reflections (pilot's helmet) and better transparency representation (transparent bricks). LDD has the advantage of having proper prints the minifigures or parts in their database.
The proof is in the details when you take a closer look, the resolution at which LDD does its 'rendering' only useful for quick jobs where you may not care about quality.
Summary and recommendation
Think of it this way, with LDD as a 2 storey building that is easy to climb up and the view is just okay, while Stud.io is a 50 storey building that takes a while to climb, but is takes time to reach the top but you eventually see the spectacular view. So that's my opinion, if you are looking for a starter software, go with LDD, while if you want a more professional software, Stud.io is best for you.
Where to get the software
Both software is available for PC and Mac, so that should get you started easily.
LEGO Digital Designer:
Stud.io