Both named providers use the eplus network, which has some gaps in coverage in few uninhabited areas, but there's no really big difference (see
eplus coverage map). However a disadvantage of eplus is, that they neither support EDGE (but GPRS) nor HSDPA (but regular 3G/UMTS).
In
another thread I advised a countryman of you, whose phone doesn't support the European 3G-bands at 2100 MHz, to go for a T-Mobile or Vodafone-based provider as they do at least have EDGE, but your N82 supports European UMTS and so you could get internet access with 384 KBit/s on eplus' 3G-network.
Anyway, if you prefer the T-Mobile network, check my recommendations on
this thread, but be ready to be charged € 1-2/min for calls to the US. Except for solomo pro and Blauworld all prepaid providers have crazy international rates.