Omnigraffle is still hands down the best tool for wireframing. While many IAs and UX professionals have been using Sketch, that's not the right tool for the job. Sketch is for prototypes—not wireframes. Here's what makes it superior:
1. LIBRARIES: You can save templates and UX elements you create to reuse (in your style) that are a simple drag and drop away. I don't know about you, but I hate recreating things like Contact forms, maps, social icons, etc. Having a vast library of your own work (and the work of others via the Graffletopia community) is a huge timesaver.
2. VARIABLES: The bottom of my wireframes, flows and sitemaps all include a copy block of the project title, canvas name, modification date, page number, etc. I type none of this. It;s auto-inserted and auto-updated by the software.
3. SHAPE MODIFICATIONS like Adobe Illustrator's Pathfinder tool. Sometime you really need the right shape of comment bubble or notched-arrow navigation state. Make as many as you want. Save them as custom shapes and they become part of the system for use whenever you need them.
4. SHARED LAYERS. Love these. Put your navigation on a shared layer and it will appear on all your new canvases within that document. I usually add an additional layer ABOVE the shared layer as an active state.
5. PRESENTATION MODE. Don't have an InVision account? Shame on you! But if you can't afford one, relax. You can make your wireframes clickable like a real website and in presentation mode, you can run through the site, full screen and each element you hover over will automatically highlight itself. In a pinch, I've done this many times and clients respond well to it. I use a thick bright outline that reminds them of the hover states they see in a certain usability testing tool we all know and love.
6. SELLING I.A.: Let's face it. Wireframes from tools like Balsamic look like a child did them. I know that's kind of the point, to keep the IA from looking too designed, but try explaining that to a client who is new to wireframes. You will have a migraine from explaining to them for the 18th time that no, the site won't look like this, and yes, the lines will be straight in dev. Omnigraffle wireframes just look better and they sell themselves to clients.
7. EXPORTING. Yes, if you are forced to export to Visio, or (shudder) open a Visio file, you can. I;ve done it many times and the scars have finally healed. You can export to PDF, BMP, EPS, PNG, HTML, JPG, PSD, SVG, TIFF, Visio XML, all three Omnigraffle doc types and OmniOutline.
8. GANTT CHARTS: Why would anyone use Omnigraffle to make a timeline when Office does this perfectly well? Simple. Ever look at a MS Project doc? Hideous and impossible to read when projected on a screen. I've recreated Gantt charts in OGP with beautiful colors, easier to read typeface choices and better spacing and guess what? Won more business, Not to get off on a soapbox, but don't make your audience strain to read something on the screen. If you start your slide with, "I know this is an eyesore but…" you've failed. Really. Omnigraffle solved that for me.
9. DRAG AND DROP INTO OTHER APPS: I regularly drag selections of charts, images and sitemaps, etc. directly from Omnigraffle and drop them into Keynote and Powerpoint slides. No problems. They scale beautifully and don't experience color shifts that sometimes occur with other apps.
10. INFOGRAPHICS. Sure, Canva.com is cool, but it can't REALLY create true infographics (yet). OGP can and they can look every bit as good as if they were done in Adobe Illustrator or Sketch.
There's little to dislike about Omnigraffle to be honest. Everything just works. My only complaints are these:
1. ACTIVE AND HOVER STATES: If we can have shared layers, we should be able to set active and hover states to objects and navigation.
2. DOCUMENT STYLES: While I can save and have access to thousands of pre-built page and app elements, it would be nice to set up document styles (colors, typefaces, logos) that are used throughout a document without assigning them manually to each element (or resorting to the paintbrush tool). Admittedly, this is a rare use case for me and probably others, but it has come up where I was given wireframe requirements (links must be this color, lines must be #ccc, all text in Helvetica Neue, etc.)
Think about your needs as an IA or UX professional before investing in any tool. If you primarily do prototyping, try Sketch. If you do more icon or illustrative work, Adobe Illustrator is your best friend. If, like me, you do both to those, but MOSTLY do wireframes, sitemaps, user flows and are required to sell them to the client in person, you should strongly consider Omnigraffle Professional (not the regular version which is missing a few critical features you'll want).
Information Architecture, User Experience, Infographics, Business Presentations. These are all areas I have successfully used Omnigraffle Pro for and will continue to use it for.