Gen 3 vs 4?

Hello and welcome to PriusChat!

It depends on what you're looking for in a vehicle. Here are some pros/cons.

Gen 3 (2015)
Pros:

• Last year of the generation (typically the most reliable. There is the head gasket issue but I think it's more prevalent in 2010-2011 models)
• More cabin storage space (two gloveboxes, larger front storage bin under flying buttress, underfloor cargo storage bin and underfloor cargo side storage bin)
• Temporary spare tire in all trim levels
• Available solar roof option (for ventilation while parked as well as remote A/C capability)
• Soft-touch steering wheel controls with "Touch Tracer"
• Variable speed rear power windows (or "soft close" if you prefer)
• Available PHEV model (could be cheaper than the regular Prius and you still have a larger battery for more regen but note replacement will be costlier than the regular Prius)

Cons:

• Basic rear torsion beam suspension
• No door pockets (just water bottle holders)
• Lots of hard plastics on the door panels and dashboard and gloveboxes - easily scratchable
  
• Heated seats are only available in one heat level (unless you get the Plug-in version)
• Rear door armrests are too low (and some found the front ones too low)
• Need to look for a rare Prius Five w/ AT Package if you want radar cruise control and Pre-Collision System (autonomous emergency braking)
• Noisy on the highway (The 2009-2013 Corolla is quieter)

Gen 4 (2016)
Pros:

• Much improved handling and ride comfort (and additional of a double wishbone rear suspension)
• Much stiffer chassis
• Lower centre of gravity with the hybrid battery relocated from the cargo area to below the rear seats
• Larger cargo area (at the expense of hidden storage bins)
• Much nicer interior (more soft-touch materials on all trims except the base Two/Two Eco. Touring models have contrasting stitching and contrasting vent surround trim pieces)
• Quieter interior (Four/Four Touring include acoustic driver's and front passenger windows)
• Much improved seat comfort (though check it out as some still found it uncomfortable)
• Much improved LED headlights
• More suitable for taller drivers (lower seating position plus taller ceiling for driver and front passenger)
• Much easier to attain higher mpg (50-52mpg on the highway with our 2016 Touring and 57mpg city) compared to Gen 3 (50-55mpg city, 47 mpg highway)
• Darker green tint for better solar insolation (might not matter if you intend to dark tint your windows but from the factory, the green tint is darker and there's better heat absorption and reflection with the Gen 4 windows than the Gen 3).
• Slightly improved forward visibility around A-pillars compared to Gen 3

Cons:

• Upper trim levels (Four/Four Touring) have no spare tire
• Lower seating position (if you prefer sitting higher up)
• Few cost cutting measures (no upper glovebox, no door scuff plates)
• No TSS-P on Two/Two Eco trim levels
• Small glovebox

That's all I can think of for now.