While the older 500 series Kirbys have an undeniable mid-century charm, I don't like the idea of shake-out bags. I prefer the convenience of replaceable filter bags (thus my disdain for modern bagless plastivacs). For that reason, I prefer Heritage and newer models. I really like my Heritage (1HD) with its sporty orange bag, but I find it annoying that it takes a different type of filter bags from my two G-series machines. I have the piece to retrofit it to take the newer type bags, but I'm waiting to do it until I've used up the last of the oval opening bags I have on hand. Of course, all that depends on whether I ever get the machine back from my girlfriend. She "borrowed" it about two years ago when her Oreck bit the dust.
All in all, I prefer my G5 and G6 (I like them equally) for their power and the ease of use provided by the Tech Drive.