I've used Mobil 1 since my engine was rebuilt years ago.
There's anecdotal evidence repeated by more than a few that suggests if you switch to a full synthetic sometime during the engine's life, you'll exacerbate oil leaks. Well, since I started with this full synthetic and never had issues, it's what I go with. If you haven't used a full synthetic and your engine has not been rebuilt, now is no time to start.
The particular formulation and content of that formulation has changed over the years. It is pretty clear that our engines demand high levels of zinc and phosphorus, lubrication additives that have slowly been weaned out of many motor oils, with the exception of specialty oils.
Last time I bought the Mobil 1, it was on sale at Walmart and was less than USD $25.00 for 5 quarts; this is price comparable to any oil out there suitable for our cars. The only grade of Mobil1 with the requisite level of additives is the 15W-50 formulation. (well, there are some others, such as racing oils, but see the chart. The 15W-50 is the easiest to find, though not always easy.)
Curiously at the local auto parts store, a single quart of the 15W-50 was around $8. Always better to get it in the 5-quart jug, and when it's on sale...