"Are they powerful enough (3 Watts) ? Are they reliable ?
Which one should I buy ? The AAA X3 or AAA X 2 ?"

IMO power, raw light output is seldom an issue, few if any flashlights are suitable as searchlights. There are a few rather expensive HID lights that are adequate searchlights but they aren't small or light and duration is short.

In my experience almost all of the use will be within 20' or so and mostly within arms reach. Within arms reach the evenness and light distribution is a primary concern. A light that puts all the light into a focused point can be tough to work with if you trying to illuminate a larger area like when your reading a map.

On the other hand a light that spreads its light over a wider area is fine for maps but it can be frustrating for detail work. Some of this is countered by the ability to focus the beam but some don't do either well or the light is uneven and spotty in either or both settings.

The other thing to watch for is color rendition. Does green look like green under this light? Reading a map or working on electronics, where wire color is critical, requires good color rendition. Reenacting the tense scene in the movie where the guy has to decide to cut the red or blue wire is a great way of building drama but it sucks in real life. LED lights can be all over the charts.

The good news is that the LED Mini-Mags are pretty good. The ability to focus or spread light are good and there are very few artifacts. Color rendition is good with a slight bias toward the blue end. Up close this isn't enough to cause any confusion.

A question is: Do you need 3 Watts? The amount of light is strong verging on too strong. Operating in the dark a dimmer light is easier on your night vision and wider situational awareness. Too bright a light means when you look into the dark you will see definite spots. The down side of this too bright goes along with shorter battery life.

Another thing to consider is cost. The 2-AA LED flashlight is going for around $25. An alternative is to buy the 2-AA incandescent Mini-Mag for about $9 and installing a Nite-Ize LED conversion lamp for $5. The Nite-Ize conversion is dimmer but plenty bright enough for close work and camp jobs. Color rendition is more yellow but perfectly acceptable for map reading and reading color codes. You lose the ability to focus the beam but the spread is a nice balance between flood and spot with very few artifacts or unevenness.

Up side is that you get adequate light for arms length and camp jobs, a bit longer battery life, and a flashlight that costs about $14 versus one that is a bit better as a focusable searchlight, has more raw power, slightly better color rendition but shorter battery life and a $25 price tag.

Owning and using both they both seem reliable. With a slight edge going to the LED Mini-Mag. Of the several Nite Ize units I have installed at least one has a burned one out of there LEDs burned out. It still works and puts out enough light but it shows both weakness and strength. Weakness that one out of three LEDs on the Nite-Ize conversion unit is out but strength in that the LED Mini-Mags have just one LED each so a single failure would end the game for those units.

Personally I find the 2-AA units to be best for my use. The LED Mini-Mag 3-AA units are too long for my liking. The 2-AAA units are thinner and lighter so if weight and bulk are important you might want to go that way but I think your right in assuming your going to get significantly shorter battery life. IMO the 2-AA units are a good compromise between handy with a nice heft and small enough to ride in a belt sheath, pocket or kit well.

A 2-AA flashlight also rides well in a Nite-Ize headband, about $7, and makes it into a nice, off to the side (Borg-like), headlamp. I never liked headlamps because they aren't user friendly used in the hand and they don't pack well.