How are you determining ARV and Rent when analyzing deals? Listening to the podcasts and reading posts, this process gets mentioned all the time but seems to always get glossed over.

For ARV comparative analysis, I have been using median of $/sqft of similar sold properties within the same neighborhood (defined by major roads/freeway, zoning, school district, major geological features aka river and zip code). However, this method does not take into account the size and value of the lot. I have tried determining the ratio between the value of the land and the value of the house itself by going through the tax assessments but the net result is wildly different from the previous stated method.

For determining rent, i have been using services like rentometer.com and only using data from the same neighborhood. The range of data is fairly limited without going back to 3 years of rental history... which I think is making the net result fairly unreliable. Also, i want to know if you think $/sqft matter more or number of bed/bath matter more in setting rent.  

Would love to get some guidance on the nitty gritty. Not looking to become an appraiser, but it would be good to refine and systematize this process.