It's up to you OP. If it matters to you that you go to a RG uni then you should go, if not go with the second option. Just make sure that you're comfortable with the final decision and that it is not somebody-else's.
Russell Group unis tend to undergo lots of additional high quality research meaning that they bring in more money. This can have a big impact on the facilities available to an undergraduate, for example, the labs might have invested in a particularly cutting edge piece of kit that can be used by undergrads. Aside from that, the lecturers are likely to be engaged in research of high quality meaning that you're being taught by someone who really knows what they're talking about. This may differ from a non RG uni where someone courses hire professional lecturers vs. research academics (the former of which might actually be better at teaching than a research academic tbh).
That's not to say that these things aren't offered at non RG unis, but rather that they appear with greater frequency within the RG.
Aside from that, unless you're applying for something like law you won't be held back because of going to a non RG uni. Non RG unis actually leap up the league tables all time so your uni might retrospectively increase in prestige.