Really, any game in the series is fine to start with except Origin, which was conceived as a direct, very tightly connected prequel to I and II and is ideally played after them. Other than these three games, the main stories throughout the series are all independent - however, there is still interconnected lore and occasional (nonessential) references to other games.
If you want to play in an order that lets you fully experience the evolution of the series' gameplay while also ensuring you'd be able to understand every reference and lore connection on your first playthrough, I'd personally suggest release order - that is:
I and II Chronicles
VI: The Ark of Napishtim
The Oath in Felghana (remake of III)
Origin
Seven
Memories of Celceta (quasi-remake of IV)
VIII: Lacrimosa of Dana
(PC versions are all definitive.)
V has yet to receive a modern remake, and the original game is both barely relevant to the rest of the series and not very good. However, a remake's been teased - just wait for that unless you're curious.
If you just want to start by trying one game that I think is the single most perfect encapsulation of what the series is all about, consider Oath in Felghana. That said - there are three main distinct styles of gameplay throughout the series. I, II and the original versions of IV are top-down 2D and use the "bump system", which means that you attack enemies simply by running around and hitting them at the right angle, with no dedicated attack button. Napishtim, Felghana and Origin use the so-called "Napishtim engine" and are in 3D, with an attack button as well as the added ability to jump, which allows for more complexity and variety in level and enemy design. Seven, Celceta and VIII use the "party system", meaning that for the first time, you can swap between playable characters on the fly, each with their own fighting style and skills. These games also did away with jumping in favor of rolling until VIII, which has both. They tend have a heavier focus on story and cutscenes than the previous games.
Also, Digital Emelas' advice on this subject is very misleading and can be safely ignored. Honestly, they have no idea what they're talking about on some of this stuff, particularly with regard to claiming the series is intended to be played in chronological order for best understanding of the story and
especially recommending to play Napishtim so late, which is just nonsensical. If you followed their story order, you'd play three games that make reference to Napishtim to some extent before playing Napishtim itself.