I had been using an HTC myTouch Slide 4G (doubleshot) , and the MTS3G (espresso) before that.
It was great, I would always win at the little online "pictionary" games since I could type out the answer faster than practically anyone else. Also, it was good for reading in a supine or other odd positions, because I could set it to only switch to landscape mode if the keyboard was slid out... it's a constant annoyance to me when other phones switch orientations because the accelerometer is giving readings it doesn't cope with well.
The MTS4G was not supposed to run Android 4, but thanks to CyanogenMOD... http://trumblings.blogspot.com...
Gradually, all of the apps on it got slower and less responsive, and I would gradually get rid of widgets and apps that would run into the background until I just had the bare essentials... Chrome, Maps, and Hangouts. But what finally did it in was that the SD card would get corrupted every time I let the batteries run all the way down.
Finally broke down and picked up a Nexus 5. The screen is big enough, esp. in landscape mode, to hunt and peck out the keys with reasonable accuracy. Unfortunately, Google hasn't made every app work in landscape mode, and some critical things (like the launcher and the frickin' Google search widget) force you to enter stuff on the tiny portrait mode keyboard. I think CyanogenMOD's Trebuchet launcher app was better with this, and I'm eagerly awaiting it to go stable on the Nexus 5 so I can switch over.
I've also been looking for a good Bluetooth keyboard case, but haven't found one yet. There are several good-looking ones for the Nexus 7, though. That would certainly scratch the itch for me. Of course, not many Android apps have good keyboard support, but they're out there... Jota+ , VXConnectBot, etc.
As an aside, after the last update to 4.4.4, my wife's Nexus 4 started getting noticeably less responsive too. Hoping it's just a matter of going through and clearing some of the Dalvik cache, and not because Google is (intentionally?) making older devices obsolete faster by adding in too many bloated features in their core apps :P