Well... no response. So I did come calculations:
Assuming what I found at yahoo autos is correct:
Jetta Wagon TDI base:
140hp/235 lb-ft
$25775
33 ft^3 cargo
92 ft^3 passenger
125 ft^3 total
30/41 MPG EPA
2.0L
Toyota Prius Base
177 hp/377 lb-ft (gas + electric)
$21100
16 ft^3 cargo
96 ft^3 passenger
112 ft^3 total
48/45 EPA
1.5L
Toyota Camry Hybrid
333 hp/337 lb-ft (gas + electric)
$25350
11 ft^3 cargo
101 ft^3 passenger
112 ft^3 total
33/34 EPA
2.4L
So, lets set this up as MPG per n where n is a variable. Let's make the results as x/y for city/highway. The results will be given as Jetta; Prius; Camry Hybrid and are as follows:
MPG/HP:0.21/0.29;0.27/0.25;0.10/0.10
MPG/TQ:0.13/0.17;0.13/0.12;0.10/0.10
MPG/k$:1.16/1.59;2.27/2.13;1.30/1.34
MPG/cargo:0.90/1.24;3.00/2.81;3.00/3.09
MPG/passenger:0.32/0.44;0.49/0.46;0.32/0.34
MPG/volume:0.24/0.33;0.42/0.40;0.29/0.30
MPG@Normalized Volume (100ft^3): 24/32;42/40;29/30
MPG/engine L:15/20.50;32/30;13.75/14.16
So, let's see... the winner is:
MPG/HP (higher is better): Prius (city), Jetta (highway)
MPG/TQ (higher is better): Prius/Jetta tie (city), Jetta (highway)
MPG/k$ (higher is better)

rius
MPG/cargo (lower is better): Jetta
MPG/passenger(lower is better): Camry/Jetta tie (city), Camry (highway)
MPG/volume (lower is better): Jetta (city), Camry (highway)
MPG@normalized vol (higher is better): Prius
MPG/engine L (higher is better): Prius
So the rationale is:
MPG/hp - lower the number, the better youre doing per output power (take the inverse and you get more HP per MPG)
MPG/tq - lower the number, the better youre doing per output torque (take the inverse and you get more torque per MPG)
MPG/k$ - the higher the number the more fuel economy youre buying, and the better value you are getting within reason
MPG/cargo - the lower the number, the more efficient you are on a volume of cargo handling basis
MPG/passenger - the lower the number, the more efficent you are on a volume of passenger space basis
MPG/volume - the lower the number, the more efficient you are on a basis of what you can haul on a total basis - take the inverse and you get more volume hauled per MPG.
MPG@normalized volume - since all volumes vary, let's look at the numbers per 100 ft^3.
MPG/engine L - the higher the number, the better your engine is roughly on a per size (and notionally per fuel input) basis.
So, overall, it looks like the prius is generally the winner, and Id say the Jetta is second place, with the Camry in third. However, that doesnt say it all. If you need volume, the jetta is a winner. If you want passenger space, the camry is a winner - the prius isnt really a contender on the metric of how much cargo or passsenger space you get, though for what you do have, it does great. It seems that overall for a practical car, the jetta wins, for a decent, super-efficient car, the prius wins.
And I think we all knew that already...
JMH