Wakkanai and Islands?

We have a few nights in Wakkanai during the first week in October - is it worth while to do a day trip to these islands, returning on the same day http://www.heartlandferry.jp/english/index2-1.html
Can we get around using a local bus on the island? Which island is nicer?

We have a few nights in Wakkanai during the first week in October - is it worth while to do a day trip to these islands, returning on the same day

Yes, I think they are by far the most interesting thing to see in and around Wakkanai.

Can we get around using a local bus on the island?

Public transportation is infrequent. It may be a challenge.

Which island is nicer?

I personally prefer Rebun. I find it has the nice walking trails. And when visibility is good, you can see Rishiri, which is a very nic sight.

Japan-guide.com users give Rebun a 92% rating and Rishiri a 87% rating.