The main difference is 3-9 weeks before certain lifts are reached.
Both are alternating with 3 workouts a week.
SL is work sets of,
(A) SQ 5x5, BP 5x5, RW 5x5
(B) SQ 5x5, OHP 5x5, DL 5x1
Thus, 37-41 work sets or 185-205 work reps a week.
This contrasts with SS 2nd edition,
(A) SQ 5x3, BP 5x3, DL 5x1
(B) SQ 5x3, OHP 5x3, PC 3x5
Thus, 25-29 work sets or 115-125 work reps a week.
So that SS has 56-68% the overall work volume of SL.
However, it should be noted that while SS2e has you start with a weight where "the bar has started slowing" and deload after a third session stalling, SL (in its last public edition, anyway) had you start with the empty bar, and change to 5x3 after your first stall.
A typical newbie to barbell training will have a "bar has started slowing" of 30-80kg (lower end for lighter deconditioned females, middle for males or females who've been doing sports, higher for larger males doing sports). Let's split the difference and call it 55kg, and assume a person in a 60-80kg bodyweight range.
With SL starting them on 20kg, the person is going to have no trouble doing 5x5 for a while; adding 2.5kg a workout, it will take 14 workouts or 5 weeks to reach the 55kg SS would have had them starting with. By this stage the person will of course be stronger. Both lifters with ordinary rest and nutrition will probably stall for the first time around 90kg, give or take 10kg. As noted, SS will have you deload, and SL have you drop two work sets and change to 5x3.
Thus, SL and SS have you get to the same place in the end, it just takes longer with SL because of Mehdi's insistence on your starting with the empty bar. This insistence comes about from the simple fact of coaching experience. Mehdi assumes that the lifters he's advising are as clueless as him and will have no real coach - so they need to start easy and take time to get the form right. Rip assumes people are self-motivated and will seek knowledge, and have a competent coach somewhere around if not during each workout - so they can start a bit harder.
In terms of online resources, SS has many free articles and videos, and questions can be asked of Rip freely; SL has a few free articles which you can get if you give him your email so he can spam you, and to get access to the forum you must pay so you can get the advice of people squatting a 20kg plate or two a side. As well, the single Mehdi offers relationship advice in his forums.
BtB is correct that SL is focused on teh abz.
Athletic Club East - curing iron deficiency
Current trainees' best lifts: ♀ 130/72.5/160 at 68kg, ♂ 205/120/220 at 105kg