Never run an Aciera before, but i am sure they are very nice. Have plenty of expirence with Deckel FP2's and FP3's and it is hard to imagine the Aciera being any nicer from an accuracy or operational stand point.
I have spoken to this before, but the great leap a Deckel has over most any other european tool room mill and that includes Aciera, Abene, Maho, etc is the "System". Deckel made enough machines and lots of accessories for those machines, so that today there is still a fair supply around. (just visit the current Reliable auction selling Deckel accessories on e-bay) Now i did not say the Deckel stuff was inexpensieve, but it is out there and for a price you can get just about any immaginable accessory that Deckel ever made. Don't think you can say that about Aciera accessories.
If the goal is to have a very fine tool room milling machine coupled with the pride of owning something fairly rare then your Aciera is a good choice!
If you want to have greater flexibility, a wider range of avaliable accessories and are willing to move down on the rarity scale, then the Deckel is a better choice...
Of course if you got the Aciera for a steal and it came with a cabinet full of tooling and accessories then all bets are off!
Have fun with your new machine, hope it works well for you and you enjoy it!
Cheers Ross