Depends on your needs. I've used DME many times, I've used a towncar service many times, I've used Mears shuttle once. So, here are my approximate times with each...
DME..average of 70 mins from gate to resort. Most times were right around that hour mark, with one trip taking close to 90 mins.
Towncar....with carryon bags only, it took as little as 45 mins. Walked to level 2, met driver, down to level 1 and into the vehicle.
With checked bags, it took between an hour and 70 mins..dependent on how long it took my bag(s) to come through.
Mears shuttle..took it to the Dolphin since DME doesn't go there. Took about 85 mins. I had no checked bag though...so you would have to add in another 15 mins for that. We made multiple stops before hitting WDW proper. I did enjoy the ride though...met some fun people and had some great conversation.
So, long story short, a towncar will save you about 30 mins if you have no checked bags. If you do have to go to baggage claim, a car service will be a bit less time than DME.
With DME you do have to factor in possible line wait times....but you don't have to worry about your luggage either.
If you don't want to bother with lines, riding a bus with others, and want a more 'special' type experience and don't mind paying for it, go with a car service. I always just factor in 90 mins of travel time...gate to resort worst case scenario. Then, I have that extra money to spend on food at WDW!!