I have owned previously:
2005 IS250 - great car if there is not more than 2 people in it (not a lot of leg room in the back). It has great road feedback and a sporty feel to it. Drove it for 3 years - only did annual maintenance on the car at the dealer.
2011 GS450h - loved the torque and the size (not the size of the boot though). Comfortable car to drive on a longer cruise. During the 4 years I did annual maintenance at the dealer and had the water pump changed
2016 GS200t F-Sport - The only good thing was the look of the front of the car. The car was not very sporty nor it was very comfortable. I didn't like the engine at all. Did only annual maintenance.
2018 LS500h F-Sport - This brings me back the joy, performance and comfort of the GS450h.
I have thought of getting myself an older IS-F for a Sunday car to bring back good memories with a punch, but we'll see about that.
It is hard for me to give you a good answer, but it depends on your preferences:
1. If you want space, comfort and power - go with GS450h
2. If you want an experience and joy - go with IS250
3. If your options are IS250 or GS300, then I would choose IS250 (if size is not an issue. 4-people driving in the car daily is not so comfortable)
I hope it helps!