I used to look at it to see what others thought were great machines. Interestingly, some of the top machines I DO love, while others -- not so much.
My advise is that going to a barcade local to you such as The Oviedo Bowl in Oviedo (Orlando) Florida, an arcade like Gamevault in Morristown NJ, or a pinball museum such as Modern Pinball in NYC and spending $50 - $100 to play a variety of well maintained games is the BEST way to research what you like. Play everything -- even the titles you have not heard of and/or think the theme sucks -- because you never know what you will or will not like until you play it.
Supporting operators is a solid investment and with the cost of pins on the rise it is increasingly important to know what YOU really like and the money you spend figuring this out (having fun I might add) will definitely SAVE you the cost of making an expensive purchase mistake.
I'm interested in hearing others opinions on this - and great question OP.