I've recently started 5-3-1 and never done westside, so FWIW:
I believe westside is extremely partial and band oriented, to the extent that if your form is not tight, and/or your ability to critique yourself accurately isn't pretty good, you will just end up buying bands and chains that you thrash yourself against to very little in the end. It's equipment intensive and expert or higher lifter imperative.
5-3-1 is for the common man. Sub maximal for the most part so no worries about spotters or equipment. It's primal in that your max rep attempts are done because you choose to go for it, not because that's the day you had optimal spotters and gear.
Also and more importantly, 5-3-1 has tons of variations that get around your particular lifting peccadillos. Need to bench and squat twice a week? Do wendler's fullbody. Need to Deadlift once a month? Do Wendler's with partials except every third week. Want to progress faster? Skip deloads or periodize your main lifts in cycles so that you only max one at a time.
I think I'm in the intermediate level and I can see value in either method.
At a certain point it's a matter of taste. Some say potatoe, some say potato.
But I do think Westside is better saved for the more way more experienced athlete.
I am Anton Zdravko Martin!
Best meet lifts: Sq 150 Kg (330 lb), Bench 120 Kg (264), DL 160 (352) @89 Kg (197)
Best gym lifts: Sq 375, Bench 280 (pause), DL 385 @205 or less
Goals beyond my wildest dreams, 600 Kg raw total, 200/160/240
Hack away at anything which isn't essential. Do what you love, and do it often. Fazc.
Everything competes for recovery so more assistance is not always the best idea. miked96