The HRT Microstreamer appears to be much better reviewed. I own the Objective 2 + ODAC and their original CYMOBB altoids amplifier and both are great so I am sure the C5D is very good too.
One advantage the C5D has over the HRT Microstreamer is that it has a bass boost toggle/button. The CYMOBB has a bass boost button that works very well so I am sure the bass boost on the C5D is great as well (many times bass tailoring on these kind of devices doesn't work well at all, sometimes making the option totally useless). The HRT microstreamer doesn't appear to have a bass boost.
However, the microstreamer does appear to review better than the C5D IMO. I can't give an opinion since I don't own the microstreamer or the C5D but I don't think you can go wrong with either device.
One thing I can add is that JDS Labs products are known for not coloring the sound much at all. It makes the sound louder but doesn't add highs, lows, etc. unlike many other devices. They are very neutral which is great if that is what you want. The HRT microstreamer, based on reviews, seems to color the sound more which is what I am looking for myself as I want thicker lows, better mids, etc. Of course, as I mentioned, the HRT microstreamer doesn't have a bass boost which could be a make or break thing for some people as the C5D does.