Honestly it really depends how competitive you want to be. I'm mostly a narrative player, but I do follow the competitive scene pretty closely.
I love the Guard, love the average dude holding the line. Narratively, in my very narrative focused area, I've got a very solid winrate. The combat box is pretty good, and is a good chunk of an army right there. It is the newest models to, which some will like but others might not.
At 500 points there really isn't that much balance. There is the new combat patrol rule set, designed specifically for combat patrol vs combat patrol. Its actually a pretty solid rule set, but requires you to be facing other combat patrol.
But if you prefer more competitive, I have some unfortunate news right now. In 10th, they're not the absolute bottom of the barrel but they are pretty close. A recent balance patch might be changing it up, but for most of the (young) edition Guard has been stuck playing a mostly artillery based army if they want to be competitive. Not entirely, there's some wiggle room, but the most effective army meta wise has been a big block of artillery just kinda sitting in the same place and raining destruction on the other side of the board. An effective strat maybe, but not a very fun one. For either side. The balance change should hopefully fix some of that, it did make tanks more effective.
But the edition constantly shifts, so things come and go. And honestly if you're starting out I suggest not worrying about the meta and competitive to much. Pick units you like the look of, and try a few games. Work out some strategies and just get some games in.