A lot of the bench plans you'll find online are primarily for woodworking - benches designed by woodworkers for woodworkers. That means you'll be doing plenty of work on the table saw and cutting some fairly complicated wood joints like half laps, cross laps, dadoes & grooves just to get the bench built. It also means the some of the plans might call for hardwood (not dimensional lumber), which will give you a practically indestructible bench. If that's what you really want or need, go for it. Otherwise, you'll need to look a little deeper to find an easy-to-build project that uses inexpensive pine and simple DIY tools.
The most notable difference between bench plans is the approach to building the top. Apparently there are more ways than one to make a large, flat surface on which you do your work. I like to narrow those choices down to two: the hard way, and the easy way. The hard way is to glue up a lot of individual boards (usually hardwood) to create a solid worktop. That means you'll be doing some careful prep work to the panels before gluing them together - lots of sanding and possibly some edge planing to get the pieces smooth enough to glue together. If you've never glued up solid wood panels, you might want to read up a little on this technique before taking on the project.
The easy way to make a bench top is to find something that looks like a table top and simply nail or screw it down to your completed frame. An old, solid wood door, for example makes a very nice bench top. And who doesn't have an old door sitting around somewhere in the basement or garage? Another easy option is to buy a thick piece of plywood and simply cut out the size you need for the top. If you have a fairly sturdy frame to start with, a plywood top will work fine for most work you'll do in a garage or basement shop.
See my favorite Bench Plans