I spend a lot of time working through basing questions as they have such widespread consequences.
I want the figures to be as close to one another as in real life, but I also want flexibility to use with several games I have in mind and others I haven't come across yet.
25/28mm figures ranging between 14th to 16th century (plus Tolkien) is what I'm deciding about now.
I should say I expect to be furnishing both sides in 90% or more of the games I play.
A few games I have in mind are Gore's Medieval Warfare, Hail Caesar/Pike & Shotte and Field of Glory.
Default or fall back footprint size is 20mm per man, but even here, do I do individual square, individual round, 40mm square, 60mm x 40, etc. I lean toward square individual or strips 1 rank deep, which I realize is old fashioned.
On top of this, as I do some dry tests 20mm sometimes feels like too much space. In 28mm scale I figure it represents about 3 and 3/4 feet square. For 18th century this would be right out, but it also doesn't look quite right for swiss pike, for example, or even HYW dismounted knights. I'm thinking 16mm feels a bit better (representing 3' in real life), which lends itself to 50mm x 20mm or 50mm x 40mm bases with 3 or 6 men to a base.
Perhaps not coincidentally what I arrived at for my 18mm FIW after long debate is 30mm x 10mm, three men to a base. I'm fully satisfied with that decision. The decision I'm making today has more widespread consequences, though, as I have a number of 28mm armies currently and planned.
Generally I think the closer you pack them in the better. I'm really not a fan of putting fewer men on a stand than fit a la DBA.
50mm x 40mm would work fine for the games above. I lean toward 50mm x 20mm though, except for pike and maybe some others, as I like the flexibility of more granular stands.
I'm far from decided though. I may just go with individual 20mm bases, or at least for things that aren't pike.
In addition to any other thoughts people have I'd be curious how appropriate you think the 3' footprint is for various medieval and renaissance types, aside from skirmishers.
Also, any pitfalls that may await me. Already I have some various Swiss types on 20mm bases which I don't expect to rebase, so if I adopt the 50mm standard there will inevitably be some fudging needed here and there. And I have some bigger figures like Front Rank that look ok on 20mm square.