I have owned both, I bought my GP100 in the 1990's, I owned a Colt Python as well, I stopped shooting the python because I liked the GP100 better, gun loves heavy bullets especially 158grn soft points and hollow points, my wife did not like automatics liked my GP100 so we bought her an SP101 as it is lighter and easier to conceal, love that little gun for CCW great pistols both of them can;'t go wrong in my opinion whichever you buy, the GP100 I had was a 4" where the SP101 had a 2" with fixed sights