ORIGINAL: Steve.
I still use my 3PB Magnum ! We bring it when my son brings a friend. How many Spekies will be around in 20 years ? The 3PKS 2.4g is still a good choice but if you can swing the extra money the 4PK will be more future compatible with the extra channel. You must be getting a Losi and I'm sure it's a decent radio especially for RTR. If the DX3S proves to be a good radio for you, there's no reason you can't just pick up extra receivers for other cars. You could also sell the Spekie and really defray the cost of a 3PKS or 4PK. We have five Futaba transmitters, the 3PB, 2 3PJS, a 3PKS Synth, and a 3PKS 2.4g along with a dozen or more different receivers and haven't had a single failure with a Futaba product. I had a Airtronics M8 a while back and it was a great radio too so based on that I would recommend Airtronics also. I'd probably try a M11x if I didn't already have so many Futaba receivers.
RIght now I can get an Airtronics M11x for the cost I could a Spektrum DX3R, so I think Im pickin up an M11x.........$320 shipped seems pretty darn good price. Some of the Futabas recievers seem to have some overheating issues? Regardless. I have always been a Fubata/Airtronics fan, so I decided to go with the m11x because thereseems to be very fewcomplaints, even compared to the Futabas. Plus their surface recievers work with 6-7.4volt input and are Lipo compatible. Seems the way to go for me since Ill be doing all 1/8th and 1/5th scale kits.