In your situation, MiamiDX would be the best choice if you can get a copy of it. It is possible to use DHCP with AmiTCP/GENESiS with client software from Aminet though I had great difficulty getting that working (my home LAN uses DHCP for IP allocation so I wanted my A4000 to do that too). I'll have to try again after I've got my A4000 up and running again after its ATX case conversion.
Another thing I'd be cocerned with connecting an Amiga directly to the Internet is the lack of a firewall. Roadshow will fix this issue by having BSD Packet Filter built in but with Miami/AmiTCP i'd be stopping any non esstential services and blocking unused port access to the net. Another option is to connect the Amiga to a system that has decent firewalling/security and use that to connect to the net.
I currently do this for my A4000 but years ago before I knew about the issues I had a direct dialup connection to my Amiga and actually had a few nasty things happen to me.
If anybody knows of firewalling software for the current Amiga I'd like to know.
