Gassers don't get as many MPGs as hybrids. I drive a 2016 Prius Four, which is the current generation. When under hard acceleration in the Prius, the engine doesn't sound stressed, unlike my 2005 Prius. The Prius is a very reliable car, but the Volt has had some problems with it's engine, not much the electrical system. The Volt gets more range than the Prius Prime, has less controversial styling, and is faster. I find the Prius fast enough for highway use in, but going up a steep mountain is not what it's meant for. In stop and go SoCal traffic, I get around 70 MPG in my regular Prius. In mixed driving 70% highway I get 58 MPG driving pretty aggressively. When going over mountain passes and passing 18-wheelers, it's not fast but it doesn't make me nervous. The Prius is limited to 112 mph, 11 mph more than the Volt. I've gone 103 mph in my Prius when no traffic was around.
An added benefit to the Prius is that you get all the active safety features standard including blind spot moinotring. A cool feature is that the Prius can park itself. You only have to brake when it tells you and the steering wheel does the rest (it works suprisingly well). In the Prime you can get an almost-Tesla sized screen, which has mixed reviews (I like it). The Prime's pricing structure ends where the Volt's price starts at $34k without tax credits. When I drove and sat in the new Volt, I noticed that the interior and rear seat are MUCH smaller and cramped than my Prius. Regular Prius seats 5, Prius Prime and Volt seat 4 (Volt has an unusable 5th seat, Prime has 2 larger seats in the back). I thought the Volt and Prius/Prime drove pretty similar. Both pretty comfy rides and a small amount of road noise. The Volt was a little quicker off the line, but the engine didn't sound refined. Volt and Prius/Prime have the same safety ratings. Volt's price starts where the Prius and Prius Prime end, at $34k.
In the Prime, the trunk floor is raised by a couple inches and it seemed significantly smaller than my Prius in person. A good reason to go with the Prius is that Toyota has been making the Prius for 17 years and they have perfected their tried-and-true hybrid system. The switch from the EV to gas engine is almost undetectable, they have suppressed most of the engine noise, and the reliability is amazing. I have 250,000 original miles on my 2005 Prius and I've only replaced the battery once, the A/C compressor, and an inverter water pump as part of a free-fix recall.
Another newbie to the segment is the Hyundai IONIQ Hybrid or Plug-In, which I've heard is more engaging to drive than the Prius and gets better MPG but not by much. The powertrain is not as refined as the Prius and I'd question reliability for the first few years. Also, the Kia Niro is not as refined, but more of a conventional crossover/hatchback. It's MPG is a little less than the Prius and the cargo space is not that generous. Both the IONIQ and the Niro are faster than the Prius and give you 10 year/100,000 mile warranties. mKaresh posted his thoughts on the Niro recently on TrueDelta.
So, if you don't need the huge trunk, go for the Prius Prime, which will give you around 22 miles of EV range. When you run out of range, you can change the driving mode into "regular Prius mode" in which you get 54 MPG and often more.