I was a monthly VIP subscriber for many years and when Presto came out, I switched over to try it out as soon as they installed the readers on streetcars. I always assumed the Metropass was a decent deal compared to per ride tokens. I also knew that some months (March, December) I was paying for convenience and not using as many trips as other months.
In three years of Presto usage, there hasn't been a single month where I've done more than $130 in TTC fares. That might differ for you, obviously, but overall Presto is saving me on the order of about $300/year over the VIP program. Having the data from the Presto site is nice - it's very easy to grab a CSV and do some analysis in Excel or Google Sheets to see exactly how much I spend on transit.