Same, I only have the standard screen. I'd like to find out if its worth getting the split focus one though (for example).
The plain vanilla screen is probably the easiest to focus for me simply because it's big and bright with excellent contrast. Curious, too, about the split image version but not enough to fork over the $ when the standard screen works so well.
I've tried the Mamiya Pro-S No. 1 Matte (matte w/fresnel lens) screen, the Mamiya No. 3 Rangefinder Spot (matte w/fresnel lens & center split prism) and a Beattie Plain Matte Intenscreen (Brightscreen?) which I purchased on eBay in October for $85US. I'd have to say I like the Mamiya No. 1 Matte best of all. The Beattie is a little bit brighter than the Mamiya screens (less than 1-stop) and is not any easier to focus. Also, when you move around to, say, a corner of the Beattie viewing screen, other parts of the screen kind of black-out.
The reason I'm not sure whether I have an Intenscreen or a Brightscreen is this: http://www.brightscreen.com/intenscreen.htm I have neither the time nor the inclination to find out what's what with that. The normal, standard, simple, unobstructed, contrasty, bright-enough and unencumbered Mamiya No. 1 Matte is my favorite.
I tend to use the No. 1 screen, the all matt with the ground glass circle. It's the one for the ProS with the dotted vertical framing lines but no horizontal framing lines unlike the screen for the Pro. Because I use gridded screens in my Nikons, I bought a No. 2 'checker' screen (Also known as the Type A4 screen for the ProSD) as I thought it would help with my lack of ability to get horizons flat. It certainly does help, but the thick blue markings are something of a distraction, not like the pale lines in the Nikon 35mm equivalent. I also have a Type D cross hair screen (also known as a number 5) which is used for parallax focussing in macro, which is something I do a lot of. I got it really cheap as a clearance item. The central area does help, and parallax focussing does work, but for some reason the rest of the screen is really dark and falls off in brighness to the edges, so it not very good for composition.