I'd use a nakiri over an usaba for general vegetable use, especially you want to tackle any root veggies as an usaba is thin enough and it's single sided blade is meant for precision work or delicate veggies. Due to the nature of an usaba using it on desne veggies can result in its blade dulling quicker than expected.

Two great Japanese vegetable knives but one is meant for more general purposes vs delicate work.

A sharp chef's knife (Victorinix is well rated, affordable, and easy to sharpen). If you want to be able to work horse through tubers a sharp nakiri (Japanese style vegetable knife) or a Cai Dao (Chinese style vegetable cleaver) or even a western style cleaver would do worlds of wonder over any vegetable slicer.

An BIFL alternative to a knife is a mandolin with changeable blades. However, these require far more safety precautions than a knife and it's reccomened to wear a slice proof kitchen glove (a multi-use consumable item).