I lean towards maxing out or even hacking newer software onto my Macs, but there are occasions where I stick with the minimum or close to it.
68Ks
-Classic II: I settled on System 7.1 for this one, which is way below the maximum OS of 7.6.1, but above the minimum of 6.0.8L. I prefer System 7 over 6 and I find 7.1 to be lighter than 7.5.x and 7.6.x, but more stable than 7.0 and 7.0.1. I have Word 5.1a on here and that's about it.
-Centris 650: I went with 7.5.5 for this one, so in between the minimum of 7.1 and maximum of 8.1. 7.5.5 runs what I want to run and while it is slower than 7.1 on here, it is faster than 7.6.x or 8.1. I have Word 5.1a on here too, but I also have Netscape 4, IE 4 and Wolfenstein 3D. Whenever I want to check out a game or other piece of color 68K native software, I put it on here.
PPCs
-WallStreet (aka PDQ): I chose 8.6 for this one. This Mac shipped with 8.5, but can run 8.1 like the earlier Wallstreets. I found OS 9 to be kinda slow on here and the only OS X version I could get to boot was Cheetah. Getting USB Mass Storage support required some digging, but once I found the driver, I was able to permanently switch to 8.6 on this Mac. I primarily run Office 98 on here and use Netscape 4 for limited web browsing, but I do occasionally play some older PPC native and FAT binary games on here like Sci-Fi Pinball.
-Sawtooth: I have Leopard and OS 9.2.2 on this one. This Sawtooth has a 1.5ghz CPU upgrade in it, so installing Leopard was easy. From what I have read online, having this CPU upgrade means that minimum OS for this Mac is now Puma and OS 9.2, so I guess you could say I have the minimum OS on here too. I primarily run TFF, PPCMC, and Office 2004 on the Leopard side. On the OS 9 side I have Photoshop 7, Macormedia Studio MX 2002, Classilla, and Office 98 along with some other stuff.
-iBook G3 Dual USB 700mhz: I have OS 9.2.2, Jaguar, Panther and Tiger on this one. The minimum OS is Puma and OS 9.2.2, so I have one of the minimum OS’s plus the maximum and the in-between ones. On the OS 9 side I have Office 98, Classilla, Photoshop 6, and whatever PPC native games I feel like putting on here. Tiger has TFF, Office v.X, and PPCMC, Panther has PPCMC and Links2, and Jaguar has AppleWorks 6.
Intel
-2006 C2D MBP: This was supposed to have a dual boot of SL and Windows XP, but I somehow messed up this Mac’s ability to boot up OS X, so this one is just Windows XP. It has Office 97 and a variety of 2000s Windows software like Real Player and Microsoft Train Simulator.
-Early 2009 Mac Mini: Currently has a triple boot of SL, Mavericks, and Ubuntu, but that may change. I use SL to handle older Intel and Universal software that doesn’t play nice with Mavericks. Mavericks has Office 2008 along with Chromium Legacy and FF 78. Ubuntu is mainly for stuff that needs the latest Firefox or whatever doesn’t work on Mavericks, but does run on Linux.