When I took a job 3 years back I was still under contract for my personal line and also issued a company phone (initially a BB and later a low-end rugged Android phone). In both instances, the work phone lived on my desk in my office with calls (and texts with Android) forwarded to my personal device. The only exception was travel abroad where I could use the company phone freely, but once the company went Android I just slid the company SIM in my personal device. The company ran an ActiveSync server for Exchange Access on personal devices, so there wasn't really any functionality I was left without on my personal phone. There was a time or two I considered a dual-sim phone, but the forwarding+activesync option gave me everything I needed. If the infrastructure and policies are in place and allow for it, this might be a perfectly workable solution.

If you do have to have a second phone, I do like the idea of a Mega device for one line and a standard size device for the other. Now that I work from home and handle voice calls through a bluetooth connected cordless phone system, I've considered having a Mega phone for home use as a tablet and swapping sims to a smaller phone for travel. The Xperia Z Ultra LTE or Galaxy Mega 6.3 came to mind, with something like a Moto G LTE for travel... but I decided 8" was the perfect tablet size for around the house and ended up with a Galaxy Tab 3 8" instead... now that the Google Now Launcher runs natively on most anything, it takes a lot of the touch-wiz-ness out of the Galaxy Tab 3 8" and makes it feel very similar to my Galaxy S4 GPE.