OANDA’s spreads for cross currencies can be quite bad and fluctuate in times of news by a lot. XM has a bit of a mixed reputation. Exness seems to be the cleanest of all and are the big dogs in Cyprus especially.
If I had to pick, I would personally pick Exness.
And which platform can you suggest for scalping? MT4 works pretty good if you use it with VPS close to server location
For scalping, it really depends on how your setup is like. Eg. do you need special indicators and stuff? Having super low latency is one battle won, but is not the biggest determinant of whether your scalping strategy is profitable.
If you need a lot of custom indicators and want to build an EA to help you trade (which is recommended for high frequency trading like scalping), then you would consider MT4 as your best bet. Also, stay away from Oanda if you want to scalp, their spreads are bad and are generally better if you’re a long term trader 
For any serious scalping MT4 is just too slow. “Instant trading” takes seconds to execute while real high-frequency bots work in microseconds.
If you use MT4 I would really suggest to stick to medium-term trading
Which scalping platform can you recommend? Do you have any profound solid recommendations?
I think Exness is not good at all. Let’s be honest here. Most people on this site are new when it comes to trading. Exness has fast withdrawals, that is true but for a beginner traders I think Exness is not good at all. They control where you put your stop level as well as your take profit level. This is not good because as a trader a personally calculated stop level and a profit taking level is very important and should not be controlled by any broker but rather by you the trader. I admired their quick support but I left them only a few hours after opening an account with them. I contacted them and asked them why can’t I add a stop loss, only then that is when they said to me that it’s their regulation that you put your stop level as per their rules! I’m sure it was 450 points if I recall well. I left them immediately! RoboForex is actually far better, withdrawals are much faster than Exness. Plus you can put your stop level where you want and your take profit where you want. Exness also manipulate their spreads especially in volatile markets. I traded Gold and made $200 instead of over $400. I left after my trading session. I could stand the risk of having a brokerage company control my stop level as well as my take profit level.