These days for senior devs I just hire them as contractors. The W2 software engineer model is fine when you've got a stable long term project, but for how fast this industry moves there's a lot of "internal startup" work that doesn't work well for W2 employees. I'm finding way more interesting work and learning a lot more just floating around being the "internal startup" guy. I've built up a couple clients who know I can deliver and will try to schedule my time in advance for new initiatives. When I need more people, I'll just hire them for a week and see if they work out.
When I was hiring for W2, I'd pair program with them using a web based code editor for two hours. We'd split the work and I'd try to get them to relax and give them a chance to show off. Usually within a two hours I'd know if I was talking to quality.
If they hated pairing, they weren't going to work well on my teams anyway, so I'd make it really clear pairing was pretty much the only nonnegotiable. Everything else was on the table as negotiable, but not that. This kept expectations aligned. The ones who could pair and knew what they were doing were really easy to spot after a few hours.
New hires should treated like like pounds on an airplane. I want as few as possible to get the job done and provide resiliency to a team. A team of three always gets more done than a team of six, etc etc. So I'd aim to hire that one good person over just trying to hit some magic number.
Although clearly I got pretty tired of all the W2 games and drama. I got tired of being told to hire X people when X/3 would objectively get more done, then later being told to layoff Y people because we were spending too much. That cycle got real old after a couple loops.
Now I'm just out as a free agent with a lot of contacts who can put together a new product quickly. I've got my squad for bigger projects and they've got me. I like this a lot better. However, if you need stable income, it's not the best, you have to be really disciplined to store up grain in the good years to have it through the lean years.
