I work as a UX/UI designer for my company's web sites. After I make the designs, I send the mockups to web developers, who implement them. It's a little more collaborative than that, but that's basically the process.
Since it's been my tool of choice for a long time, I primarily use Illustrator. Especially with Google Drive's ability to display AI files, the developers have seemed happy with what I hand off to them, and since I sit pretty close to them I'm available for questions.
However, more and more I'm becoming frustrated with how often things come up like differences in how Illustrator vs. browsers render things like colors, Illustrator's total disregard for pixels (yes, I know there are workarounds, but I'm always fighting it), the time it takes to properly redline everything, and in general how different Illustrator thinks about a design vs. how browsers do.
What are some good workflows (+tools), that put your designs closer to what'll actually be implemented and make it really easy for devs to know exactly what it's supposed to look like on the web?
Even though I can do my designs in HTML+CSS, the time trade-off isn't usually worth it for most things.
UPDATE (8 months later): I've changed a few things in my process that seemed to have helped. 1) Switched over to Sketch--this app "thinks" like the web, so my designs are much closer to what they'll be implementing. 2) Started using redlining tools (e.g. Spectr) as well as Zeplin--I'm really fond of this. 3) I've started bringing developers into my process through mini design studios and discussions--this has probably had the most positive effect on our communication.