I have a real hard time going back to Poser 4 from Poser 5 - P4 seems less stable and absurdely incapable nowadays. I've found most of the extra in Poser 5 easy to learn - not harder than Poser 4, just more of it. However one must consider what you want to use it for/with. If you still intend to use it with Bryce then aside from asking "why" (important question) I'd have to say that Poser Artist (aka Poser 4 under a new name) would suit best. Part of the reason for this is that a number of the improvements in Poser 5 apply to areas that traditionally made people want to use a different program for final composition and rendering (e.g. material capabilities, renderer capabilities). Those would be lost in using Bryce, as would features that do not export well (such as dynamic hair - which is iffy anyway - and the spiffy new material abilities). If you only need Bryce to produce a landscape backdrop and/or for final rendering, you COULD consider bringing Bryce renders into Poser 5 as backgrounds, or textures on simple props, and doing your final render in Poser 5. Alternatively Vue sounds like a fairly reasonable bet...(I've not tried Vue).