I'd definitely have to agree with Auto on Bucharest. Avoid like the plague. It's a very difficult place not to get ripped-off in, especially as a non-romanian speaking foriegner.
Cluj, of your two considered options, is definitely the best. Don't, however, discount some other cities which are experiencing strong growth such as Timisoara, Brasov, Sibiu, Oradea, Iasi (the only city in Moldova worth a look in my opinion) etc.
If you're tempted by the ski resorts then for goodness sake buy land, i.e. sites which you'll sell on later to a local who wants to build a chalet. Don't touch any apartment developments. Make sure such sites are as close as possible to the ski lifts, preferably in the heart of the resort. Avoid Poiana Brasov, which is the biggest and most expensive resort, and look for value in the smaller ones such as Baisoara near Cluj or Arieseni north of Alba Julia .
Land is your best bet for rapid capital appreciation provided you buy it right (but remember it doesn't pay any rent), followed by commercial properties on main streets or in business districts followed by new build apartments.
Personally I'd also avoid buying along the Black Sea coast for the same reason that ultimately those who invested in the Bulgarian coast will come a cropper. It's absolutely freezing in the winter and the season is at absolute MAX from the end of May to the beginning of September.
Whatever you do in Romania make sure you engage the services of an expert property lawyer to check title for you. This is ABSOLUTELY essential.
Also be sure to visit at least twice before buying. Get a feel for the area you are thinking of buying in. Hire a translator for a day and then go buy the local equivalent of the 'Buy & Sell'. Have him/her go through the property small ads with you and translate them for you so you can make comparissons.
All cautions on the buying front aside I'd say that you will throughly enjoy any trip to Romania (with the exception of Bucharest) and find that Romanians are some of the warmest and most welcoming folk in Europe. It's most certainly not a land of orphanges and gypsies anymore.
Very best of luck with it!