Ethernet Shield vs Wifi Shield

Hello,
I am completely new to Arduino development.
Using Arduino Uno board, i am trying to capture image by a camera and store it in a Micro SD card. Read the image store and send an email to my gmail account with an read image as attachment. So i am confused whether to go with Arduino Ethernet shield or with WIFIshield.
I want to finish this within a week. Please help me
Thanks

This has very little to do with arduino, quite a lot to do with what is going on around it, and you are the only person who can make a sensible decision.

I would choose an Ethernet shield. They are cheaper, usually come with an SD card socket, and I believe they are easier to handle. They also require a cable. If it is inconvenient or impossible to connect to your modem by cable, then clearly the above is not a very good answer.

One option is to use an Ethernet shield connected to a WiFi repeater. This brings several advantages to the table, not the least being the ability to change horses in mid-stream.

if you are comparing an Ethernet shield with a WiFi shield - the only difference is one is wireless.
then there's the price difference.
and many Ethernet shields also have an SD card built-in.

I am completely new to Arduino development.

and

I want to finish this within a week.

Do not sit well together. It is not a plug and play exercise.

You will have to be more concerned about the camera you use. The best bet is one of those cameras that produce jpeg images. However, they work with an SPI interface as does the shield and SD card. While you can attach all three to the SPI bus you have to close down the file in the SD card, read a bit of the image, close down that device and open up the SD again and write a little bit back. So you need a camera that can cope with being closed down and opened up repeatedly without loosing the image.
Don't say read the image into memory first because you have 2K only on an arduino Uno.

Use the Ethernet shield.

The Ethernet shield offers reliable TCP communication. The WiFi shield does not.
The Ethernet shield has a decent amount of throughput. The WiFi shield is severely bottlenecked.
The Ethernet shield behaves how you expect it to behave. The WiFi shield has a list of caveats and gotchas to work around.

No contest. Go with Ethernet whenever you can.

If you must have WiFi, get yourself a Yun or an external microrouter.

Being a newbie and wanting to finish a project like this within a week is illusory at best!!!
This project will require you to do software programming.

If it has to be WiFi then get an Ethernet Shield for the reasons already outlined and connect it to a littel relatively inexpensive pocket WiFi router such as the TP-Link WR702n, which can be had for less than $20.