In the beginning I'd say bounties and skinning wolves are the fastest ways. Wolves usually travel in packs and their skins and heart go for a very nice price so it's time-effective.
Definately. There are some areas of the map where you are attacked by waves and waves of wolves, I sold 20 of them on the market today and given that yoou can get upwards of $10 for the skin, $10 for the meat and $15 for the heart, you can get some serious money. Bounties are good fun too and sometimes can net you a couple of hundred. Some of the card/dice/finger fillet games can get you a fair amount but can also leave you in the shit so don't try them unless you really know what you're doing.
Incidentally, has anyone completed the hunting challenges? I nearly shat my load when I saw that I had to knife 2 cougars, but i did that surprisingly easily. But feck me, I now have to get 5 racoons, 5 skunks (both easy enough) and 5 foxes (only ever seen one, keep thinking I've got more but its just coyotes and wolves). So I'm a bit stuck there.
Also, about the horses, buy the deeds when you can (750 if you have high enough honour, 1500 if not) because later in the game, cougars catch you unawares and kill the horse and probably you too. When my first horse died I was on the verge of tears but now I couldn't give a feck, if anything I'm happier, cause I can skin the fecker and get a shiny new one within seconds. I've got deeds for the Kentucky Saddler (the beige stallion you get in game) and the Hungarian Half-Bred, and I must say that there is barely any difference and, if anything, the first one you get is better. I've read that thre American Standardbred (only found on the last map section you unlock) is rapid and probably the best of the 3, so I'll probably nab myself one of them when I can too.
Best thing about the game is that you could play it without doing the missions, don't get me wrong, they're fun, but the random characters, random events and hunting/collecting challenges are keeping me amused for hours. I'm only a few missions into Mexico but I'd say I've played about 10 hours already. And it looks like I'm only about a third of the way through.