The physical properties of all the usual paint formulations are well documented. I was a staunch alkyd fan, particularly on wood, but recent testing (my own and independent) have clearly shown, the latest acrylic formulations are better in every way they're graded. There are a number of things to look at and that get tested or compared, but again, it's important to compare apples to apples. For example the lowest cost acrylic Ace Hardware brand house paint, just doesn't stand up against a poly modified alkyd, but if you compare the mid-range priced Ace Hardware enamel house paint ($30 per gallon) against the same in acrylic (same price), you'll find that gloss, gloss retention, density, UV resistance, hardness, tolerance to temperature extremes, mold and mildew growth are better with the acrylics. It's the binders and resins system combinations now employed, that have shown the greatest improvements in the last couple of decades.
If price is the primary goal, then yes, a base alkyd will be a bit more durable and glossy, compared to a base acrylic (both about $20 per gallon at Ace Hardware). If on the other hand, you step up into the mid grade quality products, the acrylics will tend to be the better choice. The reason for all these "improvements" is in 2005 the US government has passed some requirements, that has forced the formulators in the industry to refine and upgrade the water borne products available. It's in the last 10 years (they knew what was coming) that the biggest gains have been made.
Paint is one of the few things in life, where you actually get what you pay for. The paints I'm using cost anywhere from $80 to $600 a gallon. A $20 - $30 a gallon paint just can't compete with these types of paints, but for a home built, on a budget, less than perfect surface, might just be what the doctor ordered. Use the best paint you can afford.