The opposition to the regime started on solid footing in January when Guaido was elected chair of the National Assembly as this one declared null the "election" of Maduro a few months before. Unfortunately the high hopes of early 2019 have been dashed and many are trying to put all the blame on Guaido. This is unfair for many reasons.
First, besides getting international support of established democracies there was little that Guaido could do. Maduro may be illegal but he control the guns. Period.
Second, Guaido is no Messiah: he is the representative of a coalition, pretty much in parliamentary style. Even though he could disagree on some of the decisions of the coalition, he could not go against its wishes, not even declare against.
Third, the international support has been based on proof that the opposition is democratic and the regime is not. As such the opposition behaviour and words must always be democratic otherwise the international support, feeble at any rate, cannot hold. Talks of coups, of outright rebellion are thus banished (assuming they were possible, to begin with).
There were mistakes in the opposition are as a whole, no matter what side one takes.
If we look at those supporting Guaido, the faults are many, like bad timing or confusion is choosing which line to attack the regime. And yet, many of these faults could not be helped and are due to what is in front: a bloody regime. The merit of the opposition is that it has managed to keep Maduro on the defense all through 2019, a defense he managed, but a defense position nevertheless. Another merit is that the parties inside the opposition that have the bulk of the votes have remained within a single front. My personal assesment is that the opposition could have done better, but not much better. (1)
For those in the opposition that do not support Guaido we can write on them as two groups.
There is a small group with little popular support that has decided to seat down with the regime and try to negotiate something. Heralded by the regime in a few months they have nothing to show for. They have been a failure, a foil for the regime and only served to weaken the opposition and Guaido (but not much, thankfully!).
The other group has been more damaging, making one wonder whether its objective is collective suicide. These are those I would call radicals. Their main grief is that Guaido did not deliver on removing Maduro within weeks of his election. Discussing with them is useless, they think that all is due to a lack of leadership; they refuse to acknowledge the cards the regime has in its hands. That radical group also openly advocates for foreign intervention. Un/Fortunately for us, they are an alt-right of sorts that do most of its damage through Internet and in Caracas (and some cities). Which is their objective? Put in place a strong man that will punish chavismo. Their candidate is Maria Corina Machado, but she is not gaining much traction in polls. Meanwhile they contribute a lot in weakening Guaido without presenting themselves as a real, or even significant option.
Personally I think that all in the opposition are more or less unworthy. Their main fault to ALL is that they cannot offer a unified front and message which not only affect the will to resist of people in the country, but also delays a stronger help from overseas. The radicals though are the main offenders since they refuse to understand that no one is going to invade a country to free it from communism just to give power to a group that does not represent 10% of the electorate.
This being said, I stick with Guaido and hope for the best in 2020. His front is by far the more representatives of the opposition and through this year they have resisted better than I would have expected. And believe me, it was not a small feat: for starters about a third of representatives are either in jail or in exile.
1) I am not going to go into other "faults" of the opposition such as uncovering a few representatives in a scheme to protect some of the regime corruption. Those are minor details that are only fodder for the radicals. The main fault this year has been not to be more confrontational with the regime like naming a new electoral board, seat back the indigenous representatives, and others. These may have amount to little but it would have at least helped the image and decant the opposition earlier between "appeasers" and the real opposition.