Terry
Which rod you use will depend on the tides and amount of lead required holding bottom more than the size of fish likely to be caught. A 20lb class rod will handle pretty much any fish you are likely to catch but if fishing big tides with heavy weights then a 30lb-class rod might be more comfortable.
For offshore use I have three weights of rod:
1st is a 10-20lb ABU Conolon Pro which is a nice rod for fishing up to a pound or so of lead. It will handle all the fish you mention but may struggle with larger fish and tides. This rod is ideal for drifting offshore banks for plaice and bass.
This rod is a through action rod and locks up progressively. It is ideal for braid as the through action gives a bit of a cushion to sudden surges.
The rod I use most is a 12-30lb Daiwa TDX which is superb and will fish well in all but the strongest of tides. This rod is a tippy rod that shows up bites well, it quickly locks up and has loads of power in the lower two thirds of the blank. If you wanted just one all round rod then imo this is the rod.
Lastly I have a Penn 30lb class rod, which is a brute, to be fair I very rarely use it but it is nice to have the option for those really big tides. A big stick to beat those tides with.
Others will post about there own ideas of the perfect rods but at the end of the day we all have our own preferences. What suits me may not suit you it is a case of getting as many opinions as possible, maybe borrowing a rod to give it a go or going to the tackle shop to have a feel then you pays yer money and takes yer chances.
If you would like to borrow any of the above rods for a day just ask
Martin