They're all a bit flaky in my experience. I have an ageing Thomson that is now 7 years old and working fine. A Grundig that croaked. Bought 2 Sagems for my kids and both failed. It's the luck of the draw, especially with all the over the air upgrades.
Humax seem to have a reputation, but this is for PVR technology. I have two old Pace Pumas PVRs. One i've had for 5 years or so, the other a year. The picture is ace, but in the early days, before numerous code upgrades, these were hopelessly unreliable. At the last upgrade a few years ago they fixed the problems, so I picked up another on Pikeybay last Christmas for £35 – bargain!
Then there are HD decoders just round the corner – I think Sigmatek have one, but check that it has a DVB-2 tuner. Of course, just because a box has an HDMI output, it doesn't mean to say it's HD compliant. It has to have a DVB-2 tuner to decode HD, period.
Good luck!