acid for mixing/ sound forge for mastering
what version of acid have you been using ? I've been using acid pro 4 for years it seems to work great. It's a big step up from the cheaper versions of acid i.e acid music,dj,etc. . . the pro versions support DX fx, busses , 5.1 surround sound, video editing. . .pretty pwerfull software. Now , I don't know if it's the BEST, but I find it to be good enough.
I've heard that soundforge is best used for putting the final touches on a finished track.
Not to knock anything else suggested here , as I'm sure that they are excellent as well . .. You're probably going to have to end up deciding on a comprimise - ease of use , flexibility , price , etc. . .