The best UI design tool for fast wireframes
If rapid wireframing is what you're looking for, then Balsamiq is a great option. You can quickly develop structure and layouts for your projects with ease. The drag-and-drop elements make life easier and you can link buttons to other pages. This means you can quickly start to plan your interfaces and then share them with your team or clients. There's no free plan, but a 30-day free trial is available.
The best UI design tool for technical UI designs
Axure has long been one of the best UI design tools on the market, and is great for more complex projects that require dynamic data. With Axure, you can really focus on mocking up projects that are more technical and require extra attention when it comes to structure and data. Note that there are versions of Axure for Windows and Mac, but no web version, and no free version either.
3. Adobe Comp
The best UI design tool for iPad wireframes
Adobe Comp is the best UI design tool for those that find themselves creating and conceptualizing on the go. Got an iPad or similar tablet with a smart pencil? If inspiration strikes when you are out and about, it enables you to develop a new concept on the bus, train, plane or just sitting on a park bench.
The app is free to download and use: you just need an Adobe ID, which is also free to set up. That said, if you pay for the Creative Cloud you'll get even more use out of it, as it can seamlessly to connect you to all your assets — photos, colours, brushes, shapes, fonts, text styles and graphics — through CreativeSync.
The best UI design tool for prototyping on Mac
After its launch in 2010, Sketch quickly became the go-to UI design app amongst the professional globally. And although many rivals have chipped away at its market share since, its dominance as the industry standard has remained fairly solid to this day.
Sketch enables you to create hi-fi interfaces and prototypes, and instantly preview them on mobile devices. One of the great features is Symbols, where you can design UI assets and elements for reuse. This helps create design systems and keep your interfaces consistent. From there, you can easily export your design into a clickable prototype.
Note that Sketch is Mac only, and there's no free version. However, many still prefer the fact that you can buy it for a one-off fee, while the full version of its main competition Adobe XD requires a monthly subscription.
5. Adobe XD
The best UI design tool for prototyping on Windows and Mac
Launched in 2016, Adobe XD has rapidly become popular throughout the design profession, and now rivals Sketch as the industry standard for digital prototyping. While each app has much to recommend it over the other, XD's big attraction over Sketch is that it works on Windows as well as Mac.
If you're a keen Adobe user and new to XD, you may not find the interface very Adobe-like to begin with – it is a jump if you've been designing in Photoshop for a while. But it does stack up to the other leading tools out there, and is worth it if you are a big Adobe fan.
XD is part of the Adobe Creative Cloud collection of design tools, but there's also a limited free version, or you can subscribe to the full version as a single app.