Sketch is designed for a specific need, in my opinion, creating screen designs with tools you can reuse and share across a project. There are no extra features to get in your way or slow you down. Other products I've used are good at creating the same type of work products, but …
Omnigraffle is great for documentation, mapping, flowcharting, and other technical diagramming scenarios. It's simple enough to bang out a quick illustration and powerful enough to build complex blueprints for complicated technical systems. If you need cross-platform compatibility, though, you're probably better off looking elsewhere. If you want complex integration with data sources (ala Visio's SQL Server integration for shape metadata), OmniGraffle also falls short — but those scenarios are few and far between in my experience.
It is very simple to master and has a variety of built-in tools that allows one to begin prototyping quickly, and can be powered using a variety of plugins for presentations. However, Sketch struggles with more complex designs, particularly those where animations or transitions are desired. It also isn't a good fit for agencies that use a variety of prototyping tools, as results from importing are not predictable.
OmniGraffle is fairly simple to use, but the one thing I think it does best is working with curved lines, particularly if you are using some of the available arc templates. Drop an arc onto your page, then tell it the dimensions it needs to be, and viola! Done. Manipulating the arcs is as simple as clicking and dragging offset points.
OmniGraffle has also done an excellent job in stirring up the creative minds of many people who create templates and tools to work with OmniGraffle (not that Microsoft hasn't done so either), and managed to get the bulk of those into well organized repositories.
What it all boils down to for me is: it just works. One doesn't need to have a computer science degree to work with it either. It is as simple or complex as you want it to be.
There could be more scaffolding to support new users in getting to know how to best use all of the many features and tools it provides.
There could be more support for printing. Many of our process flows extend beyond just one page, and OmniGraffle is rather finicky about printing multipage documents.
We could use this tool more effectively if there was the ability to have real-time team collaboration. Document handoffs can be a point of missed communication, so it’d be great if we could ever have the option of working together in the same place at the same time.
Color management can be finicky. For instance, the eyedropper tool sometimes isn’t very precise.
It would be helpful if there was a built-in commenting system that included tagging where designers and developers could have real-time collaborative conversations about designs.
Sketch is only available to Mac users. This is fine internally, but an issue when working with external folks.
Sketch is a core tool for us and the cost to keep it going with our teams is low. It provides a good alternative to other screen design tools for our team members who prefer to use it.
At the end of the day, it's just simple. This goes a long way in design and goes even further when your talking productivity, intuitive design and turnover rate. It's not difficult to figure something out even if it's not something your directly familiar with, i.e. if you want to export in certain file formats or change the size of the canvas, you don't have to delay your end product trying to figure it out. Similar situations took me less than 30 seconds to solve without a Google search. That's Usability.
The support is relatively decent, and they are quick to respond. However, their releases are not great. Sketch could use more robust testing of their software before releases. Over the last four years, I have had many days lost while waiting for Sketch to patch issues with their releases. It's actually a running joke in our office. So, support, good. Releases in the first place? Not great.
use Omnigraffle for diagraming or for quick wireframe drafting
use Sketch for more in-depth wireframing that you can then flesh out into a high fidelity mock-up, export assets for production, and integrate with prototyping tools like Proto.io and UXPin.
Sketch is great for creating digital assets quickly and easily. It is simple to figure out and easy to use. It has a very clean user interface and isn't a resource hog like Adobe products tend to be. Its export feature is fantastic, generating multiple asset sizes/resolutions in one shot. For anything other than print design, Sketch is my go-to.
Sketch has had a positive impact on the amount of time my team needs to spend in meetings gathering feedback. By creating screen views in Sketch and posting to our InVision projects, we're able to collect feedback without requiring multi-person meetings.
Sketch is an extremely affordable price point with many free and inexpensive add-on options that allow me to work the way I want without spending a lot of money on additional products.
