Easy is relative, and one persons idea of easy can be hard to another. You have a coupe of options, easiest for rego purposes would be an early 308 swap, or a later model injected 304 swap. The latter would mean you'll need the extra pollution gear and electrical (wiring and computer) stuff to install,but you'd be able to pick up a relatively cheap donor car with everything you need. LS conversion is easy nowadays, you can buy all the conversion stuff from various companies and it all basically bolts straight in. Only downside is it can get expensive depending how much you can do yourself, and whether you keep it relatively stock.
As for what would be a better engine, it comes down to personal preference. LS motors are more expensive to install initially, but they have better potential then the older 304/308/355 etc. as they can be modified to make decent power with fairly straight forward mods (intake, exhaust and cam will easily see 450-500 engine hp) and still be sedate to drive, good fuel economy, and reliable. Holden motors are cheaper, keep the car true to form (original), and sound better than a LS, but getting power up near a cammed LS will mean a full rebuild with decent heads, stroker crank, intake manifold, cam, and it wont be as smooth as the LS with similar power.
You need to have a think about what your future goals are so you don't waste money on stuff you don't need. Do you want a daily driver, weekend cruiser, strip weapon, what are your plans for the car? An LS swap will probably need an engineers certificate as well, so factor that in, it will also need a brake upgrade (VT upgrade is common and fairly cheap). Your budget will play a big part.
If you have a genuine VH SLE, I would suggest keeping it factory and sticking with a 308, or 355 stroker if you want a but more grunt. First gen Commodores are going up in price at a ridiculous rate, and a clean original example will be worth more than a modified one.
