Connie..for arch viz you cant go wrong with Vray..I think more than half the arch viz industry is using it
I found it very easy to you use with bucketloads of options which(like mental ray) you'd have to be a baggins to get your head around ;)
final render is also worth looking into..I find the ease of use alongside all the advanced things it can do is great...both are incredibly fast render engines too

using vray,final render & even mental ray I've never noticed any weird stuff while using transparency alongside ambient occlusion..everything renders as expected

I've never used Kerky but agree it would be cool to have something more advanced on offer

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