As with any project, truly articulate what you are trying to achieve. When you know, seek out numerous vendors to understand their background, their present solutions and what they are investing in.
Many companies come from a data management background, then bolt on the ESP function. Others are ESPs with whom get acquired by data management companies. Smart Focus I'd say is the latter yet from my experience they do all the same things.
Consider whether you want full marketing automation. Smart Focus works on volume based pricing whilst other vendors are more inclusive in their pricing. i.e. they operate on a subscriber no. model + give you a fully integrated customer personalisation suite.
Smart Focus have 3 products. One is a traditional ESP. One is integrating the Data insights. The last stitches the previous two together called Message Cloud. If you want all three you will not see much change out of £60k+.