My issue with both these parties is they under perform. Lib Dem have made practically no progress despite the two main parties tearing themselves apart over brexit. Lib Dems have a semi retired leader and no one to come in who seems up to the job (however I do quite like Layla Moran), its also worth pointing out that they have 1 leaver among there 12 MPs. The Greens are a single issue protest party - the rest of their policies are just re jigged Labour and some quite extreme. I don't ever see the Greens making a significant dent on main stream politics at a GE as anyone who would consider voting for them would be wasting a potential Labour vote.
There is clearly a need for a centrist Pro Eu party but if the Lib Dems were up to the job they would be well ahead of where they are now in polling. The Greens are not a centrist party - they are more like a pro EU Labour of the Corbyn mold but with no great electoral appeal.
All that said they are the choice for English Remainers alongside Change who are not standing in Council elections. So LD or Gn was my choice at the local council elections and as i do a postal vote I have picked one already.
At the Eu elections I will vote Change.uk.