Plz sirs, we are the most serious of historians. We do not resort to such infantile humour whilst we examine the boners...er, I mean bones of the long deceased.
Okay, finally a proper question about history. For the first question, my favourite would have to be Flavius Claudius Constantinus, or to use his other name - Constantine III. As cool as the Principate is, I find the Dominate to be full of equally colourful characters and few more interesting than him.
As for the second question, I am going to cheat and go back further than the Empire and instead say I'd like to see the days of the Roman Republic during the Second Punic War and afterwards. The idea of seeing both Hannibal and Scipio, two of the best military strategists together in a room discussing who they think the best general of all time was would be mind blowing.