In the end, race really doesn't matter much. Most of the bonuses and penalties that come with the various races are really temporary-- after a few levels, that bit of a head start or bit of a penalty you got won't make much difference, and by late in the game, they won't make any difference at all. 100 strength is 100 strength, whether it's a male Nord or a female Bosmer, it's all the same.
That said, female Orcs are arguably the single best race/gender combination for a hybrid combat/magic character. They're the only ones in the entire game that don't get any penalties on at least one of strength, endurance, intelligence and willpower. Instead, they get a massive penalty on personality, which really doesn't matter that much as far as gameplay goes. Again though, those attribute differences won't matter much at all later in the game.
Racial abilities are a bit more important, since they're permanent, and in that, I think Orcs have an edge too. Berserk really is handy for getting out of tough situations. Playing an Orc is also the only way to have access to drain attribute for a spell or enchantment without either doing Knights of the Nine or taking advantage of a glitch. The Imperial abilities aren't so hot. If they were lesser powers, they'd be nice, but as greater powers, they're just not a big enough deal to be worth saving up for a once-a-day thing. Imperials do have very balanced stats overall though.
Really, to me, the most important thing is just appearance and roleplay. I pay very little attention to stats (other than adjusting things sometimes in character generation to make up for a penalty on something that's going to be important to the character). It really comes down to whether you want to invest your time into following this character around as an Orc or as an Imperial. Whichever one makes the most sense and/or seems the most appealing is the right choice.