VCs tend to have specializations, the best way is probably to look into the background of the individual partners. If there is a good match there then a direct approach has a fair chance of working.

I don't see much value in the various services in this domain, they tend to have outdated information, do a crap job of filtering (both positive and negative) and can be a negative signal to a VC if they are the ones making first contact. Always make sure you own the relationship from day #1, lots of these services are just leadgen for the financial service providers ('corporate finance') who would love a slice of your pie, regardless of whether or not you manage to get funding. If you do engage a corporate finance company make sure they only get paid a fixed fee if they succeed, and make sure that they are non-exclusive.