Personally, I'd want any EV I'd own to have variable regen. I'm used to driving a 5-speed stick, and there are situations (freeway cruising) where I want maximum coasting on liftoff, and others (steep downhills) where I want max. regen. Putting all regen on the accelerator pedal is a pain in the first case, as you have to find the sweet spot with your foot; it's much easier to know that if you take your foot off, you'll coast, and if you want to slow down, you can either select a higher level of regen (preferably via paddles rather than the gear selector lever) or use the brake. Chevy got this right with the new Volt, and other companies have also. Most of this is done via software, so it's no great extra expense to provide variable regen which can suit the taste of the widest possible group of customers. If you want it all on the accelerator peddle you can have it, or none, or some intermediate value.
At a minimum, I'd want at least three levels of regen, but preferably four or more; those in ( ) are optional:
5. Freewheeling, i.e. no or very little regen, equivalent to an overdrive top gear.
4. Mild regen, equivalent to 4th gear
(3). Moderate regen, say 3rd gear.
2. Strong regen, equivalent to 2nd gear.
(1). Very strong regen, equivalent to 1st gear.
Having ACC might shift my preference from level 4 to level 3, if I'm limited to only 3 choices. IIRR, VW gives you 4 levels on the e-Golf, albeit on the selector lever rather than via paddles. I forget how many levels the 2016 Volt has. The ideal would have your personal default level of regen keyed to the fob, seat memory position or what have you for multiple drivers, or at least have the default selectable, but manual selection on startup wouldn't be all that onerous. Still, that seems pretty ridiculous in this day and age, once an owner has taken possession of a car. I've got radio channel presets in electronic memory, so it's hardly any more trouble to do the same with my driving preferences, choices like normal/sport/eco modes, steering weight and feedback, regen, suspension settings etc.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].
The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.