Which dash is considered to be the best for this model?

Depends on what features you like. Most would say stay away from anything lower than -3, due to the floating hand. -3 is fine if you like the firing pin on the hammer and a pinned front sight, also these don't have the silly lock feature. Not sure when they changed to the spring loaded front sight and the frame mounted firing pin, but I have a -8 with those features, and it is a fantastic revolver, even though it has the lock.

I'm sure others more knowledgeable than me can add more insight here.

First you need to decide if you want a 45 ACP with moon clips, or a 45 Colt.  This is the only model that Smith makes in multiple calibers. The 45 ACP guns have been generally good to go, but the early 45 Colts were prone to have oversized throats.   I personally don’t have a problem with the lock, it’s the way it is and if you want certain models you’ll just have to deal with it.  And if it really bothers you, it can be removed.

I have a 625-8 45 ACP


And a recently acquired 22-4, also a 45 ACP



Also have one of the best 45 Colts made, the model 25-7

They made the 627 in both 357 Magnum and 38 Super.

I have a 625-6 (model of 1989 though in was made in the early 90's) and its been an excellent Revolver.  Was my USPSA revolver for about two years before they changed the rules.  Still shoot it in club matches occasionally just because I like shooting it so much.  45 ACP on moonclips is pretty spectacular for fastest fumble-free reloading.

Not trying to hijack but what's the going price for a 625 in 45acp these days in excellent condition?