I think 4.1 is currently the best as it has lots of preloader hacks and lets you run installed wads off of a SD card without having to set up full nand emulation. Things might have changed recently, but I don't believe 4.2 has as many preloader hacks as 4.1 does. Note that to run custom channels, including modifed/injected wiiware/vc games) from SD, you will need to install IOS60 from CIOSCORP (I use 3.5) via wad manager. BTW, if you do use the full CIOSCORP rather than just installing a few IOSes like IOS60/IOS70 I recommend you keep IOS34 unmodified.