Economies of Scale

I don't particularly care about what size cars you use with your games - but I've gotten a lot of crap over my "tiny cars," so here I present some justification for my choice.

Bases
I don't base on 5mm rounds or GW-type plastic bases. I think it makes everyone look like they are standing on a kerb.  Instead I use 1" fender washers (I actually have about a thousand black oxidized steel washers I use), and occasionally 1.5mm acrylic bases (for motorcycles and horses).  These keep the mini closest to the table top and blend away far better to my eye than the 5mm rounds.

Ground Scale

In my games 1 inch equals 5 feet. That puts my ground scale at 1/60th.  It also means that this NewRay Fiat 500 is over 16 feet long and 7 and a half feet wide.  That is a lot of movement required to round a subcompact car. Of course ground scale is easily changed and almost always slightly out of alignment with miniature scale.

Miniature Dimensions
28mm minis are poorly proportioned. By that I mean they are ridiculously wide. The biggest argument I hear for 1/43rd cars is that it looks like the minis can get in side widthwise. That is true. However I never put my minis in my cars - but they very often stand near them. So for me - height is the important factor.

28mm is a pretty inaccurate descriptor of miniature scale.  Ideally the "X"mm refers to the eye height of a standing miniature - eye height is used to avoid confusion from hair, helmets or other headwear.  Grabbing a couple EM4 Future Wars minis, it seems that they run to just about 28mm at eye level.  Grabbing a few TAG, Artizan, Foundry and Copplestone minis (in upright standing poses) shows that most measure between 28-29mm at the eye.  Taking that 28.5mm as an average and comparing it to reality - the average American male is 69.5" or 1765mm.  Normal drawing proportions of a male body is 8 heads with the eyes located in the middle of the skull at 7.5 heads height.  However the minis tend much more toward 6 heads in height... the Suit from EM4 (middle below) is 5.8 heads tall with the eyes at 5.3 heads height.  If we assume he is of average height that puts the eyes at 63.5" or 1612mm.  1612/28=57.6 giving a miniature scale (based on height of the sculpt) of about 1/57.

As I said before minis are particularly wide (not to mention 5.5 to 6 heads tall) and elevated on a base - boosting eye height by ~2mm or 7%; So I choose to scale up my vehicles about 7% to compensate. In effect that means that I lower the average height of my minis to about 5' 5", but this is replaced by the slight mound of pavement or earth they are standing on.... I can deal with that. I also use larger scale cars for very small vehicles - my Mini is actually about 1/52 and the Willys Jeep is 1/53... conversely I drop to 1:60 scale on big things like helicopters. 

In the end I have minis that can see over the roofs of sedans, and are about the same height as normal (read: no elevation kit) SUVs. It also means that my minis can even look in the side windows of an Iveco Daily or Mercedes Sprinter van - without stepping up on the kerb.