The SX 15 means that it is the older control using a FMDC board. I would stay away from that. The DX32 control would be better. More up to date, parts more readily available, Siemens drives, etc.
TNC2500 control is a lot more reliable, but thinks a bit slower and has a lot less memory but is conversational or G&M code.
Neither one is a recent machine. I would prefer to see you get a TC22 or TC30 or TC1, 2, 3, or 4.