I dont have much of an understanding on what the Merol 707 is, but to me it looks like a super automatic.
The Rancilio Silvia on the other hand is a very popular entry level machine amongst csers.
Things to think about.
The super automatic does it all for you and so if you dont have much experience and you dont want to take the time to learn it could be the way to go.
The Rancilio you will have to do more of the work yourself but the potential to make a much better cup of coffee is there.
If you bought the Rancilio you would have to factor in the price of a grinder, which a lot of people on here will tell you, a quality grinder is as important as the machine you pour the shots from.
Are you really interested in coffee and want to learn to make the best coffee you can? Because if you do, my guess would be that the Merol 707 wont satisfy you for 2 years. The Rancilio on the other hand with a good grinder and perhaps a PID upgrade down the track will last you until you want to upgrade to something more substantial.
It really depends what you want out of your coffee experience. But its best that you take the time and research what youre getting into :)
For example I started with my first $200 machine and now my coffee equipment is the most expensive stuff to my name :P