Both are great boats - A good friend of mine had a Prindle 18.2 at the same time I had my 18SX and I remember us both soloing the boats together in some reasonable wind.

Of the two you mention I'd lean towards the Hobie 18 for ocean sailing - a little more rocker, a little less power and greater tolerance of running up onto the beach at speed repeatedly (unavoidable in some ocean sailing locations). Both would work - the Prindle would have a slightly lower max wind for solo sailing than the Hobie 18, but would be faster on the occasions when you sail 2 up.

Neither boat can be solo righted in lighter wind without some kind of righting aid - such as a righting bag (either store bought or the heavy grade plastic trash bag). Righting solo in heavier wind may be possible with good technique and a well sealed mast - but I would not rely on this unless sailing with other boats who would be able to render assistance if required.

Hobie 18 used parts/sails etc may be a little more available as more boats were produced.

I would not recommend a modern 20' beach cat for solo sailing - these are typically too powerful in all but light wind for the solo sailor.

In the 18' category you may also consider the P18 classic. At 17' you have a couple more options - the Hobie 17 or Inter 17 (in a variety of flavors).

Be safe, have fun, sail fast.

Chris.