Well all I can say is Viewsonic is a well know make as well, perhaps not as good as Iiyama. Some monitors get excellent reviews and some are just classed as ok. It really depends on which one you are on about. I can't comment even if you had said which Viewsonic monitor it was as I don't have one.
As an example, if you look at the PCA mag the second choice in the sub 19" panels is a Viewsonic, its the VG1930wm and retails at £153. Their summary, its not a looker IE it doesn't look flashy or whatever but gives an excellent vibrant picture. And its cheap, and I'm sure if you hunt about you would be able to know a bit more off.
I have a Viewsonic 19" and it is an excellent monitor.
As above though i would get Your Iiyama sorted out under warranty, they are a well known and respected company, you may not get a brand new replacement but possibly a reconditioned model, thats how most manufacturers work.
Seems Viewsonic will provide only a model the same as you have. As mine was end of line they dont have any in stock in the UK. So far it's been a month & the monitor is only 9 months old. As far as Viewsonic are concerned thats not their problem! Seems that the warranty is useless & it's not even into it's 1st year!