The 40"-49" size range puts you into the large territory of television screens. Remember that you really need to be watching a TV with a screen in this sort of size bracket from at least 2m away from the screen - the optimum range being from 2m to 2.75m away.
Viewing is ultimately all done your own personal preference, of course, but the above distances are generally accepted as being sensible recommendations for comfortable viewing.
The range of second hand 40"-49" TVs for sale is likely to be extensive and you'll probably be able to unearth a TV with pretty much any type of spec or particular features in this size range.
Between 40"-49", typically takes you out of LCD territory and you are also unlikely to find much available that have only 720p resolution (especially with later models). So, the vast majority of used 40"-49" TVs for sale are likely to be 1080p, but you'll also see a good range of 4k Ultra HD models too.
Connectivity options tend to be good in this range and you'll also see some curved models available too.