I just browsed to this site for first time ever and saw this q, so had tojoin and reply. You should check out clublexus.com for great discussions on both.
I have a 2005 ls430 and it is excellent but not like new. Very reliable and repairs are not bad now that i have finally started avoiding dealer, whose labor rates have gotten out of control and throws parts at it. Be aware that gas mileage is poor. A few years ago I had check engine light 3 times and I think the dealer "fix" hurt mileage... 20+ on highway, but 18-19 mpg overall in mixed driving.

LS460 in early years (pre-2010 or so) had expensive control arms issues and expensive potential brake booster issues that might extend beyond that year, I prefer the pre-2013, but later years are probably better and remedied that. LS430 *NEEDS* timing belt at regular intervals. Beware if buying used so you do not destroy your engine from an old, snapped belt.

My car has been reliable. most strandings were dead battery: change every 2-3 years. Water pump at 130k (did they change timing belt and pump at 90k or did they heat me?) and alternator at 145k. More electronic failures (mirror, speaker, etc.) earlier. Car has on balance gotten more reliable over time, amazingly. Repairs at dealer are expensive, but i think LS460 is far worse for parts. It is a more complicated vehicle.

Despite everything I am saying, remember ls430 is at least 16 years old and you can get a 460 from 2017. 460 is more expensive for many parts. My ls430 is still a great daily driver for the 4-5k a year I drive (no commute). But I really feel filling up the tank to keep that octane mix at 91+. I did have a cat fail (supposedly, as per a code) 3 years ago, and I avoid regular 87 gas even though some others do not. They are great cars. lS430 is more reliable and simpler but potentially much older. Maintenance maters...

Just thinking to add... LS430 is not cheap to maintain either, unless you do it yourself. Brake pads are pricey and needed perhaps every 30k-40k, etc. Timing belt is $1000+, etc. Expect bills. Mirror switch gets rusted internally, could be $300... I have owned car for 13 years. First 6 was cpo with warranty. Total repairs paid after that mostly at dealer has been $4.5k in last 7 years. One stretch with 3 check engine lights in 4 months accounts for most of that, but I persevered and am glad. But timing belts, tires, brakes, trans fluid, coolant, etc, I figured maintenanc to be over $11k over 13 years on top of the repair bills, and other repairs were covered under warranty. My 6 year old Cadillac XTS has been much cheaper to keep, even relative to the LS430 at same age.... 75k miles and still on original brake pads, and no repairs yet except for pothole damage. So LS430 is reasonable but not cheap to maintain unless low miles per year or you do it yourself. I am guessing 460 is worse.

One more thing: air suspension on either car adds an enormous repair expense!! I have it on mine and am still running original struts/shocks to avoid $8k to replace (or could remove and converty). I have been lucky that my suspension is fine, but with conventional suspension would likely have changed my shocks already. Be aware!

i have  been driving a Lexus product since 1993. All have been great and have easily lasted the 250 k miles that I require. Out of all of them my 2003 has  been my favorite. My repairs have been minimal and I have done most myself ( bulbs, door lock motors, mirror switches, serpentine belt, thermostat etc). I always consult Youtube because there is always someone the who has fixed something on a 430. For things like the timing and brakes I always use the dealer. They are pricier but the job is always done right because of their familiarity with the product.

The car has 170 K on it and the only other thing that I can think that it might eventually need will be a starter but I doubt it.

I was thinking about getting a 460 AWD so I wouldnt get stuck in my driveway during a heavy snow storm but the fact of the matter is that I only get stuck once a year and also decided against it because my 430 will easily make it to 300 thousand miles.  If you decide to get a 460 buy it without the air suspension as it does not ride a well as a coil type.

All cars are expensive to maintain but the 430 will outlast them all.