Zach, I have all three and have killed deer with all three. The 44 is an absolute keeper. While I doubt I will sell my 45-70, I wouldn't get it again if I could do it over. The gun shoots ok, it is just more recoil than I care to deal with and is effectively a reproduction of the 44 Mag, at least how I load and shoot it. So far the 30-30 is a mixed blessing. It shoots some jacketed bullet loads really well, but the barrel is off dimension and it won't shoot cast worth a hoot past 1200 fps. That would be OK, but I have a 357 Maximum that is a ballistic twin that shoots both cast and jacketed pretty well overall.
The bottom line in my experience is get the 44 Magnum. There are a lot of loads available for it and it makes a good plinker and hunter. The 30-30 is a good rifle too. The 45-70 will do things neither of the others will do, but how often do you need 400 grain bullets at speeds greater than 1600 fps, and how much do you really like heavy recoil?