If you aren't towing a huge payload it is kinda pointless to spend the money on a diesel. IMHO.
Uh, mileage? With just a Smarty, my 7500 lb. '05 4WD 2500 Cummins crew cab gets 25 MPG at 65 MPH, whereas a friends '01 4WD 1500 Ram with a 360 gasser gets 14 if he's lucky.
Cummins vs. Dmax vs. Powerjoke.
I have extensive experience with several versions of all three pulling up to 30,000 lbs. at work. The best unloaded driver is the Dmax, hands down. It drives like a car. However, put a decent load behind it, say, 15,000 lbs, and you really feel it. It's still responsive, but you can definitely tell it's loaded. The 12V Cummins is the best loaded driver of the group, with the 24V and common rail right behind. While the 12V is the slowest unloaded, when you throw 30,000 lbs. behind it, it doesn't get any slower. It's about as hairy chested as it gets. The 24V and common rail, due to torque management, have a very small bit of lag when loaded to 30K, but are still brutal as shit. The Powerjoke. FML, I f'in HATE these piece of shit engines. First off, they are reliable- especially the 7.3. But **** me, they're loud and laggy! The 7.3 is the slowest and least laggy, but it sounds like an garbage truck falling off the Empire State Building. The 6.0 is a turd 'till it spools, but are unreliable time bombs. And then the 6.whateverthe****withthetwinturbos... How in the hell F*rd decided it was a good idea to pass off this festering pile of shit as anything other than a waste of metal is beyond me. Where do I start? Turbos so laggy, you have to power brake it to pre- spool the turbos so you have a chance in hell of not being t-boned when you pull out, even when you're unloaded? LOUD WHOOSHING EXHAUST NOISE? How about a mechanically complex nightmare that does everything a Cummins does, but worse? TWO freakin' turbos and it won't even hit 30 lbs. of boost, let alone peak boost before 2400 RPM (for reference, a stock common rail Cummins makes 30 PSI at 1600 RPM)? Oh, and the best kick in the balls from FoMoCo? If you have to do anything deeper than pull the valve covers, you're talking about a goddamn cab- off- the- frame job. No shit! You cannot do head gaskets on a Powerchoke without removing the cab from the frame. WTF, F*rd, WTF????
Dodge reliability- the Common Rail engines (03+) are finicky bitches. Before I even put the first tank of fuel in it, I'd get a fuel/ air separator to save the injectors, and before the first oil change, I'd do at the very least a shift kit and GM gov. solenoid conversion. The Dodge trannies are stout- the RE line is the evolution of the old two speed TorqFlite trannies from the 50's, but their main problem is lack of line pressure, which causes excessive slippage and will cook the clutch packs. A shift kit will bump line pressures, and the GM gov. solenoid conversion replaces the piece of shit Dodge solenoid with one from GM because the Dodge solenoid won't handle the increased pressures. I was running a +60HP tune on mine with the stock 48RE tranny and smoked the front clutch pack so hard, a friction disc and plate welded themselves together and cut a groove in the input shaft drum. Then, all those pieces of metal and clutch lining circulated throughout the tranny... $3100 later, I had a billet flex plate, billet torque converter, billet input shaft, billet servos and accumulator pistion, and a full rebuild on the tranny. It's good for about 2200 lb. ft. of torque now, and I'm running my truck daily at about 500 HP and 960 lb. ft. with the boost turned up to 44 PSI without any issues. Other than the tranny and fuel/ air separator, they're otherwise pretty reliable trucks. Not as reliable as the old 12V's, but much more refined. If I had to do it again, I'd probably get a '97 or '98 12V, but only because it would have cost about 1/2 of what my '05 cost. The turbo failing on an '06 at 80K is very rare... Most don't go 'till well over 200K. And u-joints? Well... it's a work truck buried balls deep in snow with a heavy ass welder in the back.

Good thing u-joints are only $20 and take a few minutes to change.
But... if you're just towing a couple bikes, get a Tacoma. Hell, even my Miata would tow a bike on a small trailer just fine.