Often, you hear of 4 rear 5.5Jx15 ET22 rims being used in the 4-wheel rotation club. However, you might also want to consider using 4 front 4.5Jx15 ET23.5 rims instead. With these narrower rims you won't be able to use wider tire sizes such as 185/55R15 and 195/50R15, but you could use 155/60R15, 155/65R15, 165/60R15, 165/65R15, 175/55R15, 175/60R15, and 185/60R15.
Out of those tire sizes, I would go for either 165/60R15 or 165/65R15. You shouldn't have any trouble finding a tire fitter to fit up to a 165 tire size on a narrow 4.5J rim, but a tire fitter could refuse to fit the wider 175 and 185 sizes from that list, as those are not officially approved sizes for the narrow 4.5J rim. You officially need at least a 5J rim for those wider tire sizes.
Vulcantire list both Vredestein Quatrac 5 (four-season tires) and Vredestein Snowtrac 5 (winter tires) in both sizes 165/60R15 and 165/65R15. 165/60R15 keeps the gearing close to standard. 165/65R15 will raise the gearing, but you would benefit from a softer and more comfortable ride. However, even the 165/60R15 will give a better ride than standard.
The limiting factor for grip on the Smart car when cornering is generally the front tires, and the 165s should give you a little more grip than the standard front 155/60R15 tires.
Vredestein Quatrac 5 and Vredestein Snowtrac 5 in size 165/60R15
Vredestein Quatrac 5 and Vredestein Snowtrac 5 in size 165/65R15
I would stick to the Vredestein Quatrac 5 unless you have problems in deep snow. However, in deep snow you might be better off with a high ground clearance car and four-wheel drive.
Saying all that, I prefer a staggered setup such as 165/60R15 front and 185/55R15 rear on standard 4.5Jx15 ET23.5 front rims and 5.5Jx15 ET22 rear rims.
Vredestein Quatrac 5 185/55R15
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165/60R15 front tires and 185/55R15 rear tires on standard rims, gives a noticeable improvement in ride comfort over the standard 155/60R15 front tires and 175/55R15 rear tires setup and a little more grip.
The Vredestein Quatrac 5 tires have a non-directional tread pattern, so can be rotated left to right and right to left. Nowadays, most four-season tires and winter tires have a directional tread pattern so can't be rotated left to right and right to left.