The 'best idea'?... is don't bother with a faceplate at all. They're an expensive waste of time tbh.
Decent HDMI cables aren't that flexible, and since most faceplates are little more than a simple HDMI back-to-back connector then what you end up having to do is to contort a HDMI plug in to the plate at the back or to cut out enough wall space to accommodate it. If you choose a thinner cable then you risk it radiating interference to the adjacent aerial cable, and there's also a risk with longer cables that they'll struggle with full HD signals at 50 and 60 Hz refresh rates that you'd come across from a console.
There are some other issues with faceplates too. The first is a simple practical problem. If you want a neat install with minimal cabling then you'll want a slim bracket to go with the slim TV, and behind it you'll want as little spare cable as possible and also wish to avoid having a HDMI plug plus cable tail sticking out of the wall. There is a way to achieve these things but it's not with a faceplate. The second issue is one of reliability, and it is a consequence of all the issues listed above. Every joint in a cable run is a potential point of weakness. HDMI is an 'all or nothing' type signal. If a connection is flaky then there's a good chance you'll lose the picture all together. Thinking about the difficulties of installing the plate then you should be able to see that you could have one cable crammed in to a wall box at an awkward angle behind the faceplate, and another HDMI cable plugged in the front which might be squashed behind the TV on its wall bracket. In my experience calling to customers who have had issues with such installations then I'd advise you side-step that headache.
The answer is really simple. Install a brush plate. It solves all the above issues.
Set your cabling in to trunking within the wall rather than embedding it in plaster, or if it's a stud wall then leave it loose inside. Use one long HDMI from the source direct to the TV. Put the plug in to the back of the TV and feed any spare cable back in to the wall: Simple; direct; neat and reliable. The added bonus is that if/when the TV is changed in the future and you find that the HDMI sockets are somewhere else on the TV then all you need do is pull the cable through a little for the new connection point.
While you're in the process of pulling cable, put in some good aerial coax (Webro WF100) rather than the poorly shielded RG6 or 'low loss' coax. If you find yourself in Currys, Maplin, Argos or one of the DIY sheds and you're tempted to buy one of their complete TV aerial cable extension kits then takes yourself outside and give your head a shake. Those are complete rubbish and you're just buying trouble with interference if you spend any money on them.
Good luck.
P.S. Read the bit below the dotted line. Thanks