Two good boats really.
I have spent a bit of time in the Surtees 5.5 (non hardtop) and they ride great for their size, a little tippy at rest which is the trade off for the better ride. The Marco looks like it will be more stable at rest which might be better for kids, but the ride probably isn't as good as a result.
Hardtop is great for kids though, keeps the wind and spray out when travelling.
I would say trim tabs are essential for either boat, with a short hull and a hardtop, tabs are key for making sure the boat runs level when there is any sort of cross wind.
Are they both 90hp 2 strokes or 4 strokes? If one is a 4 stroke and the other is a 2 stroke, then the 4 stroke could be the deciding factor for me, unless the hull with the 2 stroke already has trim tabs and much better electronics etc.