Alundra was my first PS1 game. And it is amazing, a true classic in terms of depth of story, mature themes, and solid Zelda-esque combat, before the days of combo attacks and purchasable upgrades. It can be a bit...obtuse sometimes with its fixed perspective (as far as jumping and puzzles are concerned and how it's possible to miss some collectibles) but that's just part of the old school tradition of not dumbing things down the way a lot of games do nowadays. Highly recommended.
I should replay it to see how well it's held up over the years.
Meanwhile Arc the Lad is an enjoyable albeit super short turn-based strategy title (especially in contrast to Arc 2 which is easily 10x as long - if not longer). I'd go so far as to say Arc 1 is just an introduction to the second game, both as far as story and gameplay are concerned, so I recommend waiting for both titles to be out to get the most out of the series. That said, getting the first gives a good idea of what to expect in the sequel. (As well as providing plenty of time to do the optional dungeon to unlock the secret character in both games; I found myself in the unfortunate situation of being ~30 hours into the second and realizing that I'm missing out because I didn't exhaust the first game.)