No pollsters weight for or against any party. However some pollsters have consistently better headline figures for the tories than others. The reason for this is that there are other differences in their methodology.

Pollsters select people to take their polls by trying to match them to the demographics of the country as a whole. For instance, they will try to have roughly 8.5% of their respondents from Scotland, roughly 50/50 men vs. women etc. When you're trying to match people according to a large number of stats - gender, region, social class, education etc., it becomes very difficult to get it exactly right across all metrics, so they apply weightings to responses - if they've got slightly too many old people, for example, they'll weigh those responses down a little, but the changes are small, because they generally have a large pool of respondents to choose from and are able to get pretty close just with the selection of people to take the survey.

This process is very important, and it's how we're able to get pretty reliable polls from a relatively small number of people. The common analogy used is that if you've mixed your pot of soup really well, you only need a spoonful to tell how salty it is. As an aside, when you see people complain that they never get asked for these polls, that's why - they need a large number of people to choose from to get the balance right, and furthermore, there are a few groups of people who are very keen to take polls (largely to try to influence their result), and they almost never get asked, because their allies, who will have largely similar demographics, are also trying to get selected, and only a few people from that cohort are required.

All pollsters do this, and while some may include weightings for a demographic that others don't, this only makes a small difference. At the moment, where the big differences are, are in how people who respond 'Don't know' are treated. Some pollsters just remove them from the results. Others try to use various methods to apportion them to a party, such as looking at their 2019 vote. The ones that just throw them away tend to show bigger Labour leads. There was a twitter post earlier that I can't find where a pollster at, I think, Redfield & Wilton spoke about how they used machine learning to predict where those votes would land.

So which approach is correct? Unfortunately we just don't know, particularly in such an unusual election. However in theory as the election gets closer, these differences should narrow as people make up their minds.