There is simply no comparison between IS and SS.

Have you not noticed the flurry of sales that take place at SS when you upload a new batch? Then, after a while, those 'new' sales disappear. This is because the subscription model forces a number of clients to download 'almost anything new in case they ever need it'.

By my reckoning, about 70% of sales at SS are not 'genuine sales'.

To test the water (and particularly with such an important decision to make) you should stop uploading to SS for two months. Then you will discover the true underlying long term genuine customer demand for your pictures.

In my case I reckon after two months my income will have fallen 70%.

As such, SS is 'fools gold' but IS is a blue chip investment.

I recently did an analysis of possible customer flows at the big five agencies using amongst other things the data available from compete.com.

IS announced in September it had signed its 2,400,000th member (customer) and that number now looks more like 2,700,000.

In contrast, Fotolia has just announced its 500,000th member and Dreamstime appears to be at or around 450,000.

As far as I can make out (and its a big estimate) SS has a customer base of somewhere between 260,000 and 370,000.

For many people SS is a top earner, but the underlying customer base explains why income drops so much once new uploads stop (it removes the wham bam thank you ma'am factor).

This is only my own amateur analysis, but I hope it helps.