You sure are going to get a lot of replies to this one. In my opinion the RS is easiest but costs more than the MS-20. The MS-20 is really good it seems now with the low power mads of Jon. The RS has no mods if you use Brians timer with it. Only have to add the wires directly to the sensor.. I like that combination so far. My opinion but I fixing to try the low power mod with Gantly's inhibit circuit also. MC.
I personally prefer the MS20. I feel it is real forgiving, inexpensive, and has just the degree of sensitivity I want. Have made 2 w/ RS, and wasn't particularly pleased. I have made 8 with the MS20 and love it.
The RS seems a bit easier, but the MS-20 looks like the over-all winner for low price, better range, and the availability of Jons low power / timer / sensitivity modifications. It's nice to have the option of tinkering with the MS-20 even if you don't plan to try it immediately (also - the RS sensor is apparently going the way of the dinosaur).
There is another sensor from RS that can be hacked, has low power consumption (with some mods), adjustable daylight disable, and adjustable timer (12 sec to 12 min) Costs more than the MS-20 though.
Don't forget about the Lamson. It too is setup for 9V and works very well. For sure fire operation you should build the TLC555 timer as per the instrucs on Jesse's page although i've hooked mine directly to the IC chip in the light socket and changed a few resistors to get fairly good consistency. I wasn't worried about delay though and hence the reason why i went this way. The "best" way would be to hook as per Jesse's instrucs to be sure and get consistent results.
All I have used is the RS PIR and it is real easy to wire up. I use Brians chip and Cannon owl camera. I have built six now and still going. But like MC said your going to get different opinions. Anyhow good luck and enjoy.
Stever and gantly, you are both right I believe. For my 370 now I am going to use the RS and Brians board but I am going to setup a MS-20 next and try it since all the new improvements. The advil will be important Gantley.:crazeye: