30 Mbit/s is the same speed, no matter if it runs over copper or fiber.
However, there are important link parameters other than link speed, so there may be differences. First, latency on fiber can be better than on copper depending on the line encoding - fiber requires much less elaborate encoding than e.g. xDSL. However, lower latency doesn't make the fiber faster but sensitive applications may respond faster.
Second, fiber scales much better - in the future, you can just call your provider and order more speed. Speed on copper may be very limited, depending on the line length and quality.
Third, reliability or packet loss ratio is often better on fiber than on copper. Copper is generally susceptible to EMI (depending on cable type, cable quality, link length, and environment) while fiber is practically immune.
EDIT: in regard to "elaborate coding":
Fiber commonly uses 8b/10b that causes 20% line/bandwidth overhead but next to no time overhead or delay (a microsecond or less).
xDSL variants use OFDM/DMT and QAM encoding and modulation to cope with the channel's high attenuation/low signal-to-noise ratio. Reed-Solomon forward error-correction is added to decrease the error rate, causing a transmission delay/added latency of a few milliseconds or a few thousand microseconds. Long lines also need to add interleaving which stripes consecutive packets into each other - this causes significant, yet additional delay/latency in the order of 20 ms.
In a nutshell, copper's low frequency bandwidth and its sensitivity to noise requires elaborate encoding and FEC which in turn significantly increases latency. Of course, when FEC fails and an error cannot be compensated, the required retransmission is much worse than the usual 60 ms RTT for (long-line) ADSL.