I would not worry about noise figure in general as long as it is reasonably low, say 1dB or less. The noise figure will vary across the band anyway and it is more important to have it consistently low rather than say 0.1dB at one frequency, 1dB at another and 1.5dB at another etc.
In the old analogue days I had an 80cm dish on Eutelsat 2F1 at 13 deg E and was getting sparklies on Viva 1 and 2. I had a 1.2dB NF Nortel LNB. I changed it to 0.6dB Cambridge and the results were worse on these channels and certainly there was no improvement on any other channel.
Manufacturers will try to sell LNBs on noise figure but it is better to look at reputation and other people's experiences. In places where extreme fringe reception is being attempted, then there may be difference between LNBs but you would need to look at NF response across the band, or practical results before selecting a particular type.