Spilo: with a bit of luck (ie. it stays relatively small), in can stay in there for live (depending on the tank's footprint: is it a tall or a long tank?)
If you get a rhom, you'll need to upgrade eventually, even though that would take many, many years...
And besides that, but this is just my personal opinion, spilo's look much better. Imo, a rhom starts to look really cool and menacing when it gets really big (too big for a 30g). Baby rhoms look way too plain for me...
A gold spilo on the other hand look sweet even when it is still small...