Here's my take on this. First, I have a bought new 05 Dodge Magnum R/T Hemi (2WD though) and a bought used w/48K on it 06 Grand Cherokee Overland. With these two vehicles you're comparing apples to oranges. They are totally different in almost all respects, except for the Hemi engines, which are pretty much the same. If you're looking for better mileage/performance and more room (cargo and passenger), go with the Magnum. If you're looking for 4WD capability, go with the Jeep as the AWD Magnum sits lower, does not have a low range. As far as vehicle integrity and maintenance requirements, I've found that the Jeep is a little more maintenance intensive, but the Magnum has more rattles and squeaks than the Jeep, which is totally solid. My Maggie has only 72K on it and my Jeep has 102K on it, and I am very pro-active when it comes to maintenance and service. I also have both vehicles modded to give nearly 100 more horsepower than stock....although not completely current, see signature for approximate mods. As far as summer fuel economy goes, my Maggie gets ~14-16 mpg in town and ~26-28 mpg on the highway.....my Jeep gets ~13-15 mpg in town and ~22-23 mpg on the highway. Winter fuel economy is a mile or two less all around. As far as the fun factor goes, obviously I drive the ~600 pound heavier (Jeep is nearly 4900 lbs, Maggie is just over 4200 lbs.) Jeep more, mostly because it handles better with my lowered SRT suspension, I sit a little higher, and I think it looks better. My Maggie is quite a bit quicker (again same engine mods.) by about 1/2 second in the quarter mile, and better to drive on the highway, as far as comfort goes. Also, remember the 05's through 07's of both were made in partenership with Mercedes. The Maggie R/T has Mercedes seats, transmission, and suspension, hence a little more comfort. On the highway, the Jeep is a little more tiring.
Now, here's my take on comparing your 05 and 09 Jeeps. I'll talk about what I know on the 05's (through 07's) first, then the 09's. The 05 Jeep (and Magnum) was the first year of the WK and LX platforms with the 5.7 engine. Both the 05 Hemi's (Jeep and Magnum) used the failed Chrylser Wasted Spark System, which was only used on the 05's of both. It is not a big deal and can easily be retrofitted to the late model system which does away with this system. IMO, the biggest problems with the system were accelerated spark plug wear and a rat's nest of spark plug wires criss-crossing the top of the engine. Also, some of the 05-06 Hemi's had valve seat problems that could be quite serious. I have never had a problem with either of mine (knock on wood), and I think this problem may be aggrevated by high/overheat engine temperatures. I run 190 degree thermostats in mine instead of the stock 205 degree ones, and have the cooling fans start kicking in at just over 200 degrees instead of the 220+ degree factory settings. The 545RFE transmission, in its stock form (shift schedules and torque management) on the 05-07 Jeeps were terrible. (By the way the Hemi Magnum uses the Mercedes NAG1 which is much better, has better gear ratios and more performance potential.)
Here's what I know about the 09 Jeep, which isn't much. It has been refined somewhat since the 05-07's.....better aerodynamics (maybe better highway fuel economy) and, IMO, most importantly it has the later style Hemi engine with the Eagle heads and intake....hence a little more power and probably reliability. The transmission has also been silighly improved. Also, the Nav. Unit (if they both have it) on the 09 is way better than the antique, joy stick input type on the 05.
Bottom line would be that if you go for the Jeep, go for the 09, and if you go for the Magnum, go for an 08 which is the last year they were made. Of course you'll want to do complete "look overs" on anything you buy, making sure everything works and appears to be well cared for. After you get whatever you get, do a complete major service/inspection so you will know for sure the complete maintenance status of it. Along these lines, I'll say that neither of my vehicles have ever been to the stealer or an independent, except for custom exhaust work and tires/wheel alignments. My son and I do everything else, and neither vehicle has EVER had any maintenance issues (almost 12 years for the Maggie and over 6 years for the Jeep), except for EGR Valves and thermostats. So, stay on top of the maintenance and you'll probably have a fairly trouble free vehicle.