If this is going to be your one watch, which would you choose?

I’d go for the quartz. Both nice choices!

Seiko

Tough question. Both great. You can't go wrong with any of those. In my opinion the Tissot has just a better look. I also desided for a Tissot Quartz instead of Seiko 5. But if you should buy the Tissot don't buy the black one. It doesn't fit to the shiny bracelet and looks quite boring after a while. Some fellows wrote here about their Black dial experience on the prx and wanted to change.

Better you buy Blue or White.

But I would suggest you a third alternative.

The new Citizen NJ0150 (Tsuyosa).

They combine both: The classical vibtage Rolex look and automatic movement. But in awesome dial colors for a very reasonabke price.

I would recommend the yellow or green dial.

My friend has small wrists, like 6.5 inches. I own both a Seiko 5 desskx and 40mm PRX automatic. He tried both on and the Seiko fit perfectly on his small wrists but he also liked the PRX design, that's why I chose a 35mm quartz version in the mix.  

I like the fun look of the Citizen and I have tried it on, but it will be simply too large for him. It only comes in the 40mm size.

The Tissot PRX is a beautiful watch but i am not a fan of the integrated bracelet and for that reason i would choose the Seiko.

You said he recently got interested in watches so maybe you can get him an inexpensive spring bar removal tool, a NATO or some other strap along with the watch. That way he can have more fun, "work" on the watch and maybe increase his interest in this hobby.

Ok I see.

But consider also the body size. I have a 16cm wrist size (6.3 inch) but I'm almost 1,90m (don't know US feet, but quite tall). I've tryed the small prx and it looked ridiculous, even a close up wrist shot looked ok as a picture. So don't firget the overall look.

But in your mentioned case I would rather chose the Seiko. Because I know few people who regret the 35mm prx because it was too small (but the 40mm too big).

Start him easy at first with the Tissot PRX 35mm and I second @Uhrologe statement. Don't go with the black dial.  

That was the initial idea too, he already has a few 20mm straps which he uses on his apple watch using the adapter. The Seiko comes with 20mm lugs and could make use of those straps and comes with drilled lug holes so its very convenient. Good idea on the spring bar tool, I have a lot of them that I got along with when I order straps. 

I have a gold quartz PRX and a green automatic version also. I agree on the black dial, its just dull without any light play or a texture like other dial colours in the lineup. 

The PRX is better If its intended for a gift to someone else.

The Seiko definitely going to take the crown when it comes to being a strap monster. That watch looks insanely good on every strap.

The Seiko is the better watch, but to non-watch people the Tissot will seem like the more ‘luxurious” gift.

If he’s just getting into watches and trying to get away from the Apple it might be fun to go with a mechanical option. That plus the strap issue others have mentioned is why I’d pick the Seiko. 

I bought a lot of straps after I bought the Seiko SRPE55, some dials when done right give a watch such a new look every time you put a different strap. 

Hamilton is out of budget. Plus I myself haven't bought a Hamilton yet, I would pick a bronze khaki field in a heartbeat if they proportioned the case like the new Murph, better lume formula and put a good AR coating on the glass. Even on the new murph, the AR coating is pretty useless. 

PRX with a nice dial. It’s stylish, people will go “ooh, that’s nice, what’s that” which will send your friend spiralling down this slope we all slide down together. 

That is a tough choice.  The PRX is great watch and honestly is the more interesting overall design.  But for someone with a growing interest in watches, I feel like being introduced to mechanical/automatics is a must. The Seiko is a little more conservative but still completely GADA.  It's very much a can't go wrong watch.  

There's nothing cooler for someone new to watches than seeing a mechanical movement through a display caseback, I'd go with the seiko.

GADA is an acronym, it stands for 'Go Anywhere Do Anything'. Basically a watch you can dress up and down without worry it will look out of place.

Gotcha. Thanks! 

Id go Seiko. Tried and true, and those specific SRPE 40mm 4R36 movement watches are amazing for the price! Much love & respect! 🤙

Seiko. Better wrist presence. Better suited to more real-life situations (work, play, etc). Might get them hooked on automatic movements after the soul-free feel of a smart watch. That doesn't mean I think the Tissot is a pile of crap; it's fine for what it is (ie: popular with YouTubers but ultimately and objectively, a cheap, bottom of the ladder Swiss quartz, with an integrated bracelet that's a bit annoying), and either would be a fine gift at the end of the day. But if it was me receiving it, I'd want the Seiko all day long.

I wouldn't buy either for myself, but out of those 2, I would prefer the PRX (35mm). 

It is a cool design and the lack of sapphire on these Seikos is a no-go for me. Also the 35mm PRX would be of a much better size than the Seiko for me

The srpe is just more versatile if you want something that works with more straps. 

seiko

in the end i would rather a mech watch

personally I’d go with the PRX but if this is the only watch then go Seiko. The strap Options are too good. 

Im no pro but I'd say go for seiko, its gonna last long and is an amazing watch, 
prx is good amazing design its addictive,
but for 300+ if it was me I would suggest go for this the build quality features like tough solar and bluetooth alarm and what not its indestructible 
CASIO ECB2000DC-1A Edifice Men's Watch – G-SHOCK Canada (gshock.ca) 

or another option would be this amazing automatic

Waterbury Traditional Automatic 39mm Leather Strap Watch - Timex CA

Tissot PRX but not black

The Tissot PRX is really popular, but the Seiko with an automatic movement will feel really special, especially if he hasn't experienced a mechanical movement before. The Seiko's 20mm lugs with drilled lug holes make it more flexible with strap options, unlike the PRX which has a proprietary design.

The tissot is nice but the seiko will give them the itch none of us can cure!

If he is “into watches”, I think he will appreciate the mechanical movement if the Seiko. I don’t know, but for some reason, I don’t consider the quartz PRX a “real” PRX 🤔 (And before I’d get the hate, I am wearing a quartz watch as I write this)