Well, you really need to know what is going to go trough the antenna cable.
ATSC is the new American digital television standard. As far as I know, they are shutting down analogue TV in America, so it would be smart o look for a card that has that.
NTSC is old analogue television standard primarily used in US influenced countries mostly in Asia and America. It's the good old TV you've had for decades. I would be nice to have it, but I don't know for how long it's going to be used. As far as I know, they shut down all NTSC transmitters in US back in 2009 and same trend is same in the rest of NTSC region.
QAM is a modulation technique where two analogue or two digital signals can be emitted over two carrier waves which are out of phase by π/2. I'm not so good with telecommunications, so I won't elaborate further on what it's used for, but it's very common.
FM means frequency modulation, but in this context it is used to represent analogue voice transmissions using frequency modulation on ultra-short waves. It is very commonly used for radio broadcasts. It would be nice to look for Radio Data System when looking for cards with FM. Many radio stations use RDS to transmit additional data together with music such as name of the station, name of the song, album, artist, time of the day and so on.
You won't be able to find a good answer to your question until you do some research. If you are unsure, go ahead and buy card which has all three.
Also, interesting things to look out for are:
Hardware encoders, which means that you'll have better performance when recording video in format which is supported by encoder.
Number of bits in chipset: Video will be of higher quality if you use chip with higher number of bits.
Number of chips: Some cards have hybrid chips which menas that you can look at analogue TV OR digital TV but not at the same time. Some have analogue and digital chip which means that you can look at both at the same time and some have multiple hybrid chips which means that you can look at several analogue o digital channels at the same time. Another interesting point is does card have separate FM chip? If it does, you'll be able to watch TV and listen/record radio at the same time, but I haven't seen many cards which can do that.
Another VERY important point in my opinion is driver support and programs used for watching TV. I think that buying card from a tested brand name manufacturer is important. I've had bad experience with drivers and TV cards in past. It's not uncommon that TV cards have good divers only one version of windows for example or that programs have compatibility issues with newest versions of windows or similar.
Another interesting point is remote control. Some cards have remote controls which work only with their programs, others come with windows media center certified remote controls which should be able to work with WMC too. The certified RCs are better from compatibility point of view.
I can't think of anything interesting at the moment.
Hybrid tuner means that the TV tuner chip on the card is capable of receiving both analogue and digital television, but not at the same time. You can only watch analogue television or digital television using that one chip. Cards which come with single hybrid chip are cheaper that some other available options which I will address later.
Dual tuner means that there are two TV tuner chips on the card. It's like having two cards in one. They can work independently, so you can watch one channel and record other or watch two channels at the same time.
This is where it gets complicated and why reviews are important: Some cards have two chips where one is analogue and can only receive analogue television and other is digital and can only receive digital television. Such cards are more expensive than cards with single hybrid chip. There is other option too: Some cards may come with two hybrid chips which means that you have two hybrid cards in one. You can watch or record two digital channels, two analogue channels or one analogue channel and one digital channel at the same time. These cards are of course more expensive than single tuner cards, but are nice if you can afford one.