There's no reason you shouldn't just erase a PICAXE. You can start with an 08 see how it goes.
I did an assessment of 'most capable' PICmicro in terms of best all-round platform to write any software on. It doesn't help choose the best PICmicro for any particular project but this has been very handy when having to decide which to buy or the best samples to get.
My assessment was based on a reference of DIP packaging, 4K Flash, 256 Data Eeprom, 256 User SFR ( Ram ) and having Internal Oscillator. Score on far right indicates its usefulness, the higher the better. See attached. There may be other, better PICmicro's since that list was created.
My conclusions for what to get were ...
For 14-pin use ... 16F688
For 18-pin use ... 16F88 (18X), 18F1320, 30F3012
For 28-pin use ... 16F886 (28X1), 18F2550
For 40-pin use ... 16F887 (40X1), 18F4550
The dsPic30F3012 is the only one I'm aware of in DIP form, has a different instruction set to 16F/18F, needs a completely different suite of software to normal Microchip MPASM and most 16F programmers do not support it, so probably for more experienced users only.
Four personal recommendations -
1) It's soon to be Christmas; any 'samples' Santa brings are de-facto free
2) Get three of any selected chip and expect at least one to involuntarily expire
3) Don't casually reject the 18F's
4) Buy the Microchip Pickit2 programmer