Minis with the oval bases? I'd still put a hex base under them. It helps a TON when it comes to keeping things standing (and thus unbroken) in case of an errant shirt sleeve or evil cat.
Also, for larger miniatures (such as the Seraph or Malice) I strongly suggest not wasting time on the standard Battletech base, and skipping straight to the IWM 30mm or 32mm base. I frequently put 32mm bases on minis, and it's a huge help- the base isn't a ridiculous amount larger by footprint than before, but without the sloping 'lip' anymore there's a lot more room to fit big feet and still have room for basing material.
Oh- and welcome to the forums!