I am planning on taking my boys to Philly for a 3-4 days and wondering if a stay at a hotel near the airport--Renaissance is the one I am looking at--is a good idea or should I spend a little more and stay right in the city. I was planning on parking at the hotel (as I am driving there) and taking a taxi into the city and just walking around from there.
Living just a bit outside the city across the river in NJ, I haven't stayed at any of the airport hotels so I can't help there, however I can tell you that I've looked a few times into driving into the city to stay for a night, as public transit from where we live is not a good/easy option, but the parking fees are quite high downtown (~$50 overnight) so I have not done it yet. Especially if you're not going to be using the car to get around town I don't know that I'd recommend it but you need to weigh the costs yourself.
The downtown hotels are pretty well located to the historic district and might make sense if you're going for that, but if you are planning to hit a variety of areas within the city it may make more sense to stay outside where you don't have to pay much if anything to park and get transport, taxi or train, into the city. A call to the hotel is probably best to get estimates for taxi fare to downtown to determine whether it's any cheaper than parking downtown.
Most of the historical attractions, like Liberty Bell, Independence Hall, Constitution Center, are all pretty much in the same spot, and the Franklin Hotel (a Renaissance property) would be the most convenient to those if staying downtown. I haven't stayed there so can't recommend other than it looks pretty nice, and parking is cheapest of any downtown ($28 self-park).
If you're looking for the Art Museum (do the Rocky run up the stairs!), or any other museums around there, they're a bit of a hike from the historic area, but if your boys are older and don't mind a long walk you can walk it. As with any city there are areas to avoid, especially when on foot, but the direct route during the day wouldn't put you in any of those areas.
If you're into sports and want to go down to the stadium complex, that's too far to walk, best to taxi or train. Similarly to anything in South Philly (cheesesteaks, maybe?)
If there's any specific attractions you're looking to visit I can try to offer any insights I might have.
Having stayed at the PHL Airport Marriott and the Airport Renaissance I would certainly select the Airport Marriott especially if you are flying out of the airport after your last night. The hotel is connected to Terminal B and you can clear security at that Terminal and walk to any of the other terminals inside security or simply take the complimentary shuttle from the hotel to your terminal your flight leaves from. The CL associate Nathan is nothing less than spectacular and is always a joy to visit with and talk to while you're in the lounge if you can get access. The Renaissance is a very nice hotel don't get me wrong, just not quite as easy to get to/from the airport and the train station at the airport as well.
As far as getting into the downtown area, the train from the airport to downtown takes around 20-25 minutes I believe, hassmh can confirm the travel time if you don't have a car and will use public transportation. Even if you do have a car the train is probably the best way to get there form the airport hotel.
Also have stayed downtown at the City Center Marriott, another very nice property that was bustling each time I was there, but then again if you are flying from PHL it's much nicer to be right at the airport rather than have to drag any luggage with you even if only carry-on bags.
Just to clarify IAHFLYR, from the original post npendy is planning to drive, but considering staying at an airport hotel to avoid the expense of downtown. So while convenience to the airport itself isn't paramount, the train access is likely a convenience at the airport Marriott over other airport locations. According to www.septa.org, it looks like 30 min by train from the airport to Jefferson Station where the downtown hotels are. Given the parking challenges downtown, if staying at an airport location I would recommend trying the train versus trying to drive into the city; the hotel rates aren't that much cheaper outside the city, but parking most likely is quite cheaper.
Alternatively, if you'd like to stay downtown but don't want to pay the parking fees, you could park at an off-site airport lot, take the shuttle to the airport and get a train to downtown. Much cheaper parking, can often get coupons online for $7.95/night, sometimes even less. I never thought of that before, but might give it a try sometime myself; beats paying $50 downtown to park!
I've done both and I definitely prefer being able to walk to destinations. Center city is definitely worth the extra cost, in most cities, and definitely so in Philly.
While you're there, be sure to check out the Italian restaurants in South Philly! If you do choose the airport, I suggest taking your car into the city. Parking is not that difficult or expensive, compared to a taxi.