As others have said, the Z has the comfort and the engine. The Lotus has the handling and is more raw.
For a sunday morning blast when you just want to have fun, the Exige will always be the car for me. But when I've just spent 12 hours with a client and have 200 miles to get home, I much prefer to see the Z waiting for me rather than the Exige.
I adore both cars, but they are just different. I moved to the Z so I could run my fun car daily, and in that sense it's perfect.
The biggest thing that affects my perception of the cars was how and when I drove them. The zed is driven everyday, with lots of motorway miles, lots of time with cruise on - so anything will feel duller then. Then it also has the days where it's driven properly, so I get the mixed view. The exige on the other hand was only driven for fun - driving for the sake of driving, going to fun places, at the crack of dawn on winding roads etc. So looking back I associate the Exige with fun times, not slogging along the M6.
Both great cars, just approached from a different angle.