Regular or standard version= No traction control, no multimedia steering controls, standard suspension, no sun shade, no auto lights, no passenger door controls, no 6 CD changer, no OEM navi screen, no 18 inch wheels, no auto parking, no leather seats, no seat heating, no passenger side powered seat, rear AC etc...
250G S (sports version)= Traction control (button is under the steering column, left side of steering column, light will illuminate when TRC is off), powered sun shades (very rare though), active suspension (very, very rare), sport mode button next to TRC button, suspension setting button next to TRC button as well (it will have a picture of a car shock on it), auto parking (button will be to the side of the OEM navigation screen, will be 1 inch big, will have an icon of a car turning its wheels), original navigation screen which will be embossed with no gaps and will say TOYOTA when turned on (will have radio controls, AC controls for passenger side and rear AC, auto parking instructions etc etc...), multimedia steering controls with passenger side audio controls, 6 way powered and heated leather seats (can be black or either beige), 6 CD changer, 18 inch 5 spoke alloys, trunk lip spoiler, automatic lights (like in a Mercedes or a BMW), automatic rain sensing wipers (not very reliable as they don't always detect water) etc...
300G (top of the line version. It is not usual for a 300G to have all the options but they usually do like some even don't have TRC but some do and some don't have auto parking while some do).= A top of the line 300G Premium will have the sunroof and cruise control and including all the options I've mentioned above.
Regarding suspension, Mark Xs with electronic suspension adjust their suspension according to the road you are driving on. If road is bumpy, it'll become soft. If is flat and the car is at high speed, it will choose the hard setting to give the driver more feel of the road. Ones with electronic suspension absorb bumps and are very comfortable on bumpy roads, the standard Mark X is also comfortable but there is a noticeable difference between the ride quality. The Mark X also has a speed sensitive steering wheel, it gets stiffer as your speed increases and softer as your speed decreases.
Its very rare to find a Mark X with cruise control so don't worry if you don't find one with that option. All of the features I've mentioned are options so they may vary from car to car.
Hope I was able to answer your question.
Feel free to ask anything.
Weren't you inclined towards Mercedes Benz before?