Definitely take the freeway....the strip will be a way better scenic drive but the bill will rack up while you sit in traffic forever. I would stick with a cab though and not use the bus. That is just me though. I am not a bus person. Good luck!
First time in LV we did the cab thing. From downtown to the Mirage was $25 with tip and not taking the strip. That trip cost us a fortune in cabs as we wanted to see a lot being our first trip. Since then I've always rented a car...with the right deal it will save a lot of money. There's enough free parking wherever you go (or close enough) that it isn't an issue and you have the freedom of not waiting for buses or cabs.
I'll rent a car for the first 24 hours I'm in Vegas. First it gives me a ride from the airport to my hotel (I do a "one-way" rental with the car company that has a booth at my hotel). On the way to the hotel I'll make a couple of stops to stock up on drinks and snacks for the room. I'll also hit the outlying places that I want to visit on the trip during that 24 hours. The rest of the trip is foot and bus plus a small amount of taxi like getting back to the airport.
