Hi Sandy. The reliability/longevity question of the 900 has been raised countless times already (myself included).
A lot of effort has been put into the design of this machine and thorough inspection by some of our esteemed sponsors have given it 2 thumbs up. Breville will back their product with a 2 year warranty.
The Silvia is a much simpler machine which if well looked after should last you a minimum of 10 years. If this is the longevity youre looking for then buy the Silvia.
For me its a no-brainer, if you can afford it buy the Breville. It will be an easier and nicer machine to use, it gives you far greater control over the coffee making process and greater steam capabilities. Will it last 10+ years? Only time will tell, there are certainly a lot more things which can go wrong with it.
Talk Coffee and Cuppacoffee have some great pre-delivery specials you should check out. Essentially you can get a free Smart Grinder with your 900.