Personally my favorite race are the Romulans... I love being sneeky and stealthy... and the star bases make them, in my opinion, almost unstoppable... especialy the ability for a starbase to cloak and recharge it's anti-matter, instead of draining it.
Last night, I beat the Borg set to Vicious last night 1vs1, with no cheating... and I even allowed the Borg time to recearch cubes and unicomplexes....
The way I did it was wait until the Borg are out invading one of my systems, then quick plunk a starbase in the Borg-Star gravity well. Oh, FYI, in this game both the Borg and myself were in seperate star systems....
Anyway, when the Borg came for me, I took some of my Cap ships and sent them to the Borg star, along with my starbase constructor. Before the Borg could return, I had the station built and the 1st level of Cloak researched. Then I cloaked my cap ships, and went to the nearest Borg planets and began attacking the labs and such... basically terrorist strikes... and sure enough, the Borg broke off their attack and came back to defend their system... only to find me gone again....
This is were the fun began, because the invasion fleet tried to leave again, except my cap ships and star base started seriously screwing with them... uncloaking when they're on the other side of the gravity well, so they'd head that way, then uncloak another ship somewhere else... all the while picking off whatever ships I could... mostly stragglers...
The big advantage is the ability to uncloak, hit a Borg fleet with a D'Verix Singularity vortex to cripple them, then nail them with D'Deridex Torp barrage and Norexian Nemesis-refit, and then do it again if possible... and re-cloak before they recover... this trick can do some devitating damage to even the Borg.
The biggest trick, and I maybe shouldn't be giving it away... is to bait the Borg to fight the Rommies in a star gravity well... because all of the stars recharge anti-matter so fast, it makes pretty much all the Rommie ships able to stay cloaked indefinitly.... and that ability is what can take down even the Borg...