Given the subject of this thread it is probably a good idea to review tire basics.
Diameter- 18", 19" etc is not inherently more or less durable, economical to operate although larger diameter tires do have more actual tread than to smaller diameter tires. The smaller the diameter, other things remaining equal the lighter will be the tire and the smaller the load capacity. Other things are not equal.
Cross section- 235, 245 etc is distance of one side of tread to the other in mm. The wider the cross section the more tread reaches the road. In general wider cross sections are associated with "stickier" performance on dry smooth surfaces but less good performance on rough, wet surfaces. Very wide cross sections have less resilience torrid hazards than do smaller cross sections but also have increased load capacity.
Aspect ratio- 45, 40 etc. is the sidewall depth in mm. The lower the aspect ration the stiffer the tire and the better smooth road handling will be, but aspect ration is the primary size metric for tread wear, road hazard exposure and price. The lower the aspect ration the less flexibility the tire will have so the harder the tire must work. The price of better smooth road contact is lower durability and higher price. Thus the 35mm aspect ratio of the Model S 21" tires vs the 45mm aspect ratio of the 19" means that the 21" tires have higher exposure to road hazards and wear than do the 19".
Compounds/construction- these two factors are not directly disclosed, but there are hints in tire tread wear ratings, market positioning and type of vehicle for OEM cases. The typical case is that optional larger tires generally have lower aspect ratio and are built more for dry smooth surfaces than are the smaller diameter options that typically are standard equipment. So it is for Tesla S and X.
If the choice is for "looking cool" and better handling on smooth and dry, choose the optional sizes. If durability and resilience are the primary issues go with the base. Of course, always the "sportier"the choice the more expensive the tire and the shorter the tire life.
For energy efficiency the optimal choice is typically very thin cross section, large diameter with very hard compounds. That produces very low rolling resistance, thus consumes less energy, but the thin cross section also combine to increase road hazard risk, although the hard compounds typically have long life otherwise. the prototype for this combination is the BMW i3 with the base tire 155/70R19. The optional 155/60R20 is similar. The base tire has much less road hazards, while the optional one is even harder compounds and thus lasts longer if it does not fail with road hazards. Both are famously subjects to road hazards because of the tiny cross section and tire compounds, but the optional one is far worse.
So, for Model 3 the 18" and 19" on the surface are not too much different. The major issue is whether the two are compounded differently. Personally, I would never choose the larger wheel sizes for S or X, but I might on the Model 3 because there is no obvious major difference to suggest one will be less economical or efficient than the other. My guess is that they're quite similar. When the Performance version finally comes I am sure that the optional tires will have a 'stickier' tread, maybe even a smaller aspect ratio so probably will have characteristics to the optional sizes on S and X. Right now there is not enough data to reach similar conclusions about Model 3 choices, although apparent different supplier for the two tire give clues and with the precise tire specifications we can know.
For my Model 3 I'd really like to have the wheel design of the 19" in the 18" size. Who knows, that might be a choice by the time production grows.