from wat i know about all the different ovens it is best to start with a cheap oven as used in kitchens, and then extend it with a decent temperature controller.
With a hot air oven the temperature will be relatively evenly divided, except for near the hot air outlet. Sometimes these blow too hard and blow components off the pcb.
For an IR grill like oven (these are often the smallest) you can add a metal plate to shield your pcb from direct IR and add a small fan to stir the air a bit.
The motor is preferably outside of the heated compartment, with only yhe axle sticking through.
For really low budget, a scrapped combi mircowave with a worn out microwave tube would be an ideal start. It has the cabinet with look through door, heating elements, fans, relay's and even a low voltage power supply for the temperature controller, and storage space to put it in.
From what I've heard the cheaper purpose built ovens are not so good, unless modified extensively, and the professional ovens are pretty expensive. And that is why a kitchen oven is a decent start for a diy project.