The three incher looks better. I do have a 2" 10 I will relate some 'accuracy' examples with. Once you learn the bullet drop for the particular round, if you do your part, hitting a 12"-16" steel plate at 100-110yd with the 2" 10 hand-held is do-able. It really aggrivates the hunters at the range who have spent all day trying to hit those plates with their scoped rifles - from a rest!
The longer barrel, in theory, will help tighten up your groups - but, more importantly, it affords a longer sight radius, making greater precision with your targetting.
The biggest problem - with most new SP101s - is the rough and stiff trigger. The lockwork is easily improved - much of the required work is simply removing burrs. Weaker springs help - the trigger return also securing the trigger group to the frame. A weaker spring there really helps the subsequent trigger group removal. The hammer spring can stand some lightening, too. I cleaned up my 4" .32M SP101 - and put the lightest Wolff springs in it - it still popped every primer I tried - and had a great trigger, too - really sweet - but, after all, it is just a smaller scale copy of the excellent GP100/SRH lockwork - and that from an S&W fan!
Stainz.