Try both if you can. The G&L is more flexible if you can wrap your head around the preamp. Backing off volume can even have significant impact on your tone because the output is extremely hot. Some people (possibly including you) struggle with the pre and claim it only has one or two usable tones. Completely understandable and no judgement in that statement (I do not like variable mid controls; I can wrap my head around them, but I fiddle with them too much, so I sympathize with this group). Just pointing out that it is an odd setup compared to most of the market, some love it (including me) and some do not.
I will also echo the amp comment. I have found my L2500 and L5000 sound great through most amps, but I have tried a few that sounded terrible with them. While this is true for any bass, it has always seemed more extreme to me on the MFD equipped G&Ls. Active/Passive input/switch on the amp can make a significant difference on these basses as well. Cannot prove it, but I suspect the tuning of the amplifier input is what causes the great/garbage difference to exist.
I will also echo the amp comment. I have found my L2500 and L5000 sound great through most amps, but I have tried a few that sounded terrible with them. While this is true for any bass, it has always seemed more extreme to me on the MFD equipped G&Ls. Active/Passive input/switch on the amp can make a significant difference on these basses as well. Cannot prove it, but I suspect the tuning of the amplifier input is what causes the great/garbage difference to exist.