I like the Rain Bird DV-100 and the Richdel/Irritrol 2400.
Both have been made for years with very few changes. They both are made in jartop configurations and the DV 100 comes in a non jartop configuration as well.
As far as unions go, I dont like them unless you intend on removing the valves annually. Just too many threaded connections to potentially leak. If you are concerned about future replacement, always plumb the valve manifolds so that you have room to retrofit it later by allowing ample pipe between the fittings and valves. But if you are replacing the valves, it has been my experience that you should get at least 7 years service out of them before a solenoid or diaphram replacement is necessary.

Thanks "all wet" for your reply. I was looking at Lowes and HD valves today and they sell Rainbird JTV100 and CP100 valves for about 14.00 each. They also have the replacement parts in stock as well. I know this site hates the big box stores but without a discount the supply houses are 2x more and they are a long distance drive. I wonder if the lowes and HD are acceptable for light residential use.
As far as the threaded unions go, I was only thinking about them for ease of installation. I figured I would use them on one end of the valve only and use a threaded adapter/slip on the other end. That way I would not have to did out the Valve box and dig up the pipes to give enough room to flex the fittings together. When I've fixed pipe breaks in the past I've always had to dig out around 3 feet on either side and flex the pipe upwards to couple the break. I figure I'll have to do the same with the valve. I have St. Augustine Grass so it is tough to dig up and replace. It's a lot easier with seeded grass. Unless there is a quick fix way to fit in a valve or repair a pipe, I don't know of any other way other than to dig up the yard. I called some supply houses in the past and they recommended using a threaded slip fitting coupler similar to sink drain plumbing fittings. They seem like they would be kind of lightweight and more prone to leaking than a threaded union. Thanks again for any other advise.

Do yourself a favor and go the supply house route. There are several online, and some with free shipping. (MTI) There REALLY is a difference in the quality of the two DIFFERENT products they sell, even though they may look the same to the layperson. Go with one of the two makes/models I had previously recommended. Orbit...no bueno.
As far as the unions go, I wouldn't use them on my system. I would either use some sort of telescoping repair coupling (like a "Slip-Fix") if you have the room or replumb the manifold so I didn't have to force the pipe. Look for ells in your current manifold....that's where you'll find the movement you need to replumb the valves.

Thanks "all wet", I agree that the supply valves are the way to go considering what a pain it would be to change out junk. Even if I wanted to go with the Rainbird valves from lowes and hd, which are probably good enough for my system, the ones they sell don't have flow controls. From what I've read online, the flow control can come in handy so why not get ones with the feature. One sight that does reviews recommends the Weathermatic brand. What I like about them is they will shut down if the diaphragm dies. Here in Fla. the water police give stiff fines regardless of the reason. One fine would pay for many new valves so it seems like a nice feature. I'm not sure if the Rainbird or Irritrol Valves have this feature. Thanks for your input "all wet".